At the Monte Carlo casino, a wealthy man called Joseph Morrison has just won a huge fortune at the roulette table with his lucky number thirteen. The host Madame Diabolique congratulates him but warns him that before he can cash his fortune, he must fulfil his side of a contract he signed. Morrison becomes nervous, especially when he realises that Diabolique is serious about it… Diabolique summons two of her thugs to grab him and take him away, saying that her master will receive his payment…
Jago and Litefoot are resting on the beach in Monte Carlo while drinking some wine. They are approached by Neville Tibbs, a passenger on the Fata Morgana. Litefoot invites him to join but Tibbs declines stating that he has other matters to attend to. Captain Mercer arrives and expresses how fortunate it is to be able to restock but advises the Infernal Investigators to not get too comfortable as they will set sail the next morning. To while away the time, Mercer mentions that Aubrey is organising a trip to the Monte Carlo casino. Both men decide to visit seeing as they can’t just visit Monte Carlo without checking it out, plus it would make for an interesting evening.
Sometime later, Litefoot has finished playing and calculates that he’s lost thirteen shillings to the games. Meanwhile, Jago is on a roll and continually winning, but Litefoot urges him not to overdo it. Aubrey arrives and Litefoot leaves Jago in his capable hands while he retires to the bar.
At the bar, Litefoot recognises and meets Luke Betterman, a famous doctor from Harley Street who specialises in nervous disorders. Betterman recognises Litefoot as a colleague in pathology. They immediately hit it off and get chatting.
Meanwhile, Jago’s luck is still running high, despite Aubrey’s attempts to coerce him to quit while he’s ahead. Suddenly, they hear a man shouting angrily at a woman about how she took everything from his friend, even his soul. The casino security arrives and drags the man out onto the street. Jago takes note of the rather attractive woman and leaves the table to check if she is okay.
At the bar, the argument doesn’t go unnoticed by Litefoot and Betterman. Litefoot assumes the man got drunk and couldn’t find his friends. But Betterman believes something else is going on as the security were rather quick to respond to the incident. Litefoot decides to make a few inquiries…
Jago meets the woman who was berated by the angry man and asks if she is alright. The woman assures him that she is fine and that the man has been evicted from the premises. She introduces herself as Madame Diabolique and leaves to continue her business.
Litefoot and Betterman reunite at the bar to share their discoveries. Litefoot explains that several people have been reported missing over the past several months, and the only thing that connects them all is that they all visited the Monte Carlo Casino before disappearing. Betterman learned that the angry man was inquiring after a man called Joseph Morrison, a man who had disappeared the night before. Litefoot breaks the unfortunate bit of news…all the missing people were discovered dead on a stretch of beach not far from the casino, but the beach where they landed is beneath a series of cliffs that have a reputation as a suicide spot. Litefoot isn’t certain that these men could’ve killed themselves and suspects foul play. He and Betterman decide to visit the beach to see if they can find a body to examine…
Litefoot and Betterman leave the casino to head to the beach. Suddenly, a large slab of rock from the casino roof falls off and nearly hits Litefoot. The locals begin to fuss about at the scene. Jago and Aubrey come running out to see what the commotion was, Litefoot assures his friend that he and Betterman are fine, plus he introduces Betterman to Jago. He and Betterman brush off the incident as an accident, but Litefoot quietly confides to Jago that he felt it wasn’t an accident and explains to him that he and Betterman are investigating a missing persons case. Jago decides to come with him and Betterman to investigate, while giving his winnings to Aubrey to play for him in his place.
The trio arrive at the beach and near the suicide spot, coincidently where a suspiciously large pile of sand lays. The trio dig at the sand and discover a body. After looking at the body and discovering several broken bones that happened after the death, Litefoot deduces that the man didn’t drown or die from falling off the cliff…but rather died from heart failure. Betterman agrees as he notes that the face is fixed with a look of terror, indicating the man suffered a terrible fright before dying of heart failure. Jago checks the man’s wallet and discovers that the man is the missing man from the night before – Joesph Morrison. Betterman heads off to the police station to inform the police, while Litefoot tells Jago that he wishes to investigate the Casino roof to see who or what tried to kill him…
On the roof, Jago and Litefoot find no reason to suspect foul play, as the stonework on the roof is rather old, yet they can’t rule out the possibly of a possible assassination attempt. Both men stop to think that they’re possibly overthinking things as they’re so used to danger and decide to put the matter to rest and allow the police to deal with it.
Later at the casino bar, Betterman confirms that the police have descended onto the beach to investigate the matter. Remembering the angry associate of Joesph Morrison shouting that he had his soul, Betterman recalls a rather dark story regarding whether a human loses the soul after death. He explains that a hangman he worked with once tested this theory by weighing a condemned man before hanging him, then re-weighing the condemned man afterwards to see if the body had lost any ounce of weight to determine whether or not the soul was a detachable asset.
Meanwhile, Jago discovers that Aubrey has managed to win a lot more for Jago in his absence. Madame Diabolique arrives and reacquaints herself with Jago. Seeing how much they’ve won, she offers the men a chance to gamble in an invitation only area called ‘The Dark Casino’ – a place she describes is exclusively for the very wealthy. Aubrey is hesitant, but Jago is on a high and accepts the offer and Diabolique leads them to ‘the night of their lives…’
Litefoot notices how late it is and decides its time to return to the Fata Morgana. He bids Betterman goodbye and leaves to find his friend.
Diabolique leads Jago and Aubrey through a bolted iron door into an ominously dark room lit only by candles. Diabolique introduces Jago to the Dark Casino’s gamemaster, a man dressed in cultist robes. While Jago is delighted by the spooky atmosphere, Aubrey is rather nervous. Before they can play their games, Diabolique requires the men to sign a few documents and waivers…
Litefoot is searching the Casino for Jago. A waitress informs Litefoot that Jago and Aubrey left the casino not long ago, possibly to take in the air.
In the Dark Casino, after signing a few papers, Diabolique requests that they sign a document that states that if they win at a game called the Devil’s Roulette, they must pay a forfeit. But she states that it is merely a formality and means nothing. She explains that in order to play the Devil’s Roulette, they must win all the other games before doing so. If they win at it, they’ll win an immeasurable fortune. Jago eagerly tries to sign the paperwork, but Diabolique cryptically explains that if they do win, they must forfeit to the Dark Casino’s master something they own that has no tangible weight or value – their soul…
Outside the casino, Litefoot sees Betterman and goes to ask if he’s seen Jago. He notices that Betterman is heading for the cliffs and quietly follows him. Once he reaches the cliffs, Litefoot notices Betterman seemingly disappear behind a bush. He checks the bush and finds a tunnel in the ground concealed by it. With no other choice, Litefoot cautiously enters the tunnel…
In the Dark Casino, Jago’s luck shows no sign of stopping as he wins another game, thus progressing to the next game – a dice game. Simply roll a double and you win. Diabolique hands Jago her ‘Lucky Dice’ to use and he rolls two sixes, winning the game. Whereas Aubrey’s luck isn’t shining…
Litefoot has entered the mysterious tunnel he saw Betterman enter. Not long after venturing into the tunnel, he finds Betterman. Betterman explains that he was visiting the cliffs to see how the dead bodies could’ve ended up on the beach. He reasons that there must be something on the cliffs that the bodies were brought from. His suspicions were proven correct when he literally stumbled into the tunnel. They both decide to venture together into the tunnel. Moments later, they reach the end and find a steel door unlocked. They open the door and discover what appears to be a candlelit viewing gallery. They both look down at the floor and discover a huge pentagram caved into it…they’ve stumbled into some sort of occult chamber…
In the Dark Casino, Jago is still rolling high as he has just won a game of blackjack. Diabolique informs Jago that he has won enough games to progress to the Devil’s Roulette. Jago is beyond excited as he relishes the unimaginable wealth that awaits him. However, Diabolique states that Aubrey must leave as Jago alone must play the game. She escorts him out of the Dark Casino.
Litefoot and Betterman ascend to the viewing gallery and see that the chamber is filled with occult symbols. They discover an archive filled with files and books. They both flitter through the files and discover several documents, most of which are last wills and testament documents. Litefoot becomes suspicious and sifts through the M Files and discovers a file for Joseph Morrison…
Diabolique escorts Aubrey to the casino entrance. Aubrey is insistent that he watch Jago’s crowning moment of glory, but Diabolique becomes impatient, even more so when Aubrey points to a private door and asks if he wait there. Noticing her anxious reaction, Aubrey points behind her and pretends to see Jago leaving the Dark Casino. With Diabolique distracted, Aubrey dashes through the private door and locks it behind him. He gathers his courage as he states to himself that something sinister is afoot and Jago is right in the middle of it all…
Litefoot and Betterman notice someone below. The individual in question is Aubrey, so Litefoot and Betterman come out from hiding to meet with him. Litefoot explains that they’ve uncovered an audacious scheme involving the murder of wealthy individuals and claiming their inheritances. Aubrey exclaims that is what Diabolique meant when the Casino would claim something valuable but intangible! Jago’s a wealthy man who owns a theatre with substantial value! They would claim his practical legacy! Litefoot now knows who the villain is, but before he can reveal who it is, Betterman interjects and states that the villain is…Litefoot! Litefoot and Betterman begin to argue as Litefoot states he knows not much more about the events than Betterman, but Aubrey breaks them up and tells them that Jago is about to play the Devil’s Roulette. If he wins, he will forfeit his soul!
In the Dark Casino, Jago is playing the Devil’s Roulette and upon Diabolique’s suggestion places his bet on her lucky number thirteen. The Roulette stops on thirteen…meaning Jago has won the Devil’s Roulette! Jago is overcome with excitement and glee. However, Diabolique reminds Jago of his contract…the Devil will now claim his soul!
In the occult chamber, Betterman is still throwing baseless accusations around until Litefoot tells him to stop assuming everyone he meets is a criminal mastermind! Betterman explains the true reason why he’s in Monte Carlo, he’s investigating the suspicious demise of one of his friends called James Gladwell, who promised to leave a substantial sum of money to his clinic in his inheritance. However, Gladwell and his wife came to Monte Carlo on holiday, during which time Gladwell visited the casino and promptly died after visiting, but not before having a new will drawn up which left his entire fortune and estate to a holding company in London. Betterman and Gladwell’s widow had tried to contest the will but found it to be legally airtight. And now Gladwell’s widow has only one month to vacate their home with no money or entitlements to her name. The doors to the occult chamber open and a single robed figure enters the room. The trio hide as they watch the robed figure walk to the archives with a set of documents in hand. The figure files away the documents and leaves the room. Litefoot heads over to the archive and fishes out the newest document and discovers a last will and testament signed by…Henry Gordon Jago! Aubrey explains that they were forced to sign a few documents but doesn’t recognise this one. Litefoot deduces that they slipped the will under another document so the ink from the above document when signed pressed onto the will passed onto it. Plus, with many people witnessing the signing, it would make it legally binding! They now know the process, the casino scouts out wealthy patrons, take them to the dark casino for promises of high stakes gambling, make them sign away documents which includes a fake will unbeknownst to the victim, rig the games in favour of the patron to make them forget the documents and then murder them. But Betterman points out that there was no sign of violence on the victims when they died, so the question is…how did they die? Did they really have their souls taken away?
Diabolique leads Jago into the occult chamber and prepares him to have his soul taken. The cultist leader welcomes Jago to the Devil’s Domain, then the robed cultists begin to chant ominously as the doors to the room are bolted shut. Litefoot, Betterman and Aubrey watch on from above, but are discovered by Diabolique holding a gun. Diabolique drops her French accent to reveal her Cockney British accent, she reveals that she was the one who tried to kill Litefoot and Betterman by dropping the stone slab on their heads as she feared they were asking too many questions. With the gun in hand, she warns the trio to just sit back and watch the show or she’ll shoot.
The Cultist Leader theatrically asks Jago if he is prepared to surrender his soul, as the shadowy figure of the Dark One approaches in a cloud of billowing smoke!
In the upper gallery, Litefoot deduces why Diabolique came to the upper gallery in the first place before discovering him and his allies, she was shining a limelight onto a glass slide, which in turn projects an image in the smoke to make it look demonic. The victim watches on in horror before their heart gives out and dies, then the cultists use the tunnel to dispose of the body via the cliffs. It’s all just one big illusion! Litefoot’s fear becomes alleviated when he realises that there’s going to be a distraction soon, he explains that this illusion would fool the most down to earth of people…but not someone whose job specialises in theatrics…
Down below, Jago suddenly claps and compliments the performance, but explains that he saw through the pepper’s ghost technique to create the shadowy demon and rubs salt in the wound by stating he’s seen more convincing auditions in his theatre. The cultists are incredulous at Jago’s lack of fear and the fact he saw through the tricks. Diabolique becomes overcome with rage and declares that nobody sees through her tricks! She rushes to the edge of the gallery to take aim at Jago with her gun. Litefoot and Betterman wrestle with Diabolique. In the struggle, Diabolique falls over the edge of the gallery and lands on the ground dead.
The Cultists all begin to run out of the chamber in panic after witnessing Diabolqiue’s death. The leader tries to rally his cultists to no avail. He turns his attention to Jago and accuses him of murder and reaches for Diabolique’s gun, but Jago is defiant and punches the mad cultist in the face, knocking him out.
Jago, Litefoot and Aubrey are recovering from the events at the Casino bar, but Aubrey is anxious to return to the Fata Morgana as soon as possible. Betterman arrives and tells the group that the police have begun making arrests of everyone connected to the Dark Casino on charges of extortion and murder. He further explains that he will be returning to London to help dissolve the holding company and make sure the rightful heirs receive their inheritances from the Dark Casino.
The next morning, Jago and Litefoot set sail once more on the Fata Morgana. They reflect on the night’s previous events, but begin to feel like the air’s getting thicker, but shrug it off as ordinary sea mist. After all, with all that’s happened, they could end up anywhere next!
