Los Angeles is being plagued by The Casanova Killer, named for leaving his female victims dead in their best lingerie and candlelight. Even worse is that the killer contacts Mark directly, taunting him in a sick little game of cat-and-mouse as he continues his spree. And even when Mark gets solidly on the maniac's trail, it comes to light that there may be more to the death of one of his victims than meets the eye...
"X Marks the Murder" displays symptoms of the following tropes:
- Accidental Murder: Al accidentally kills Andrew when he pulls out a gun to threaten him into giving him the promised money for murdering Dusty Wohlmann. The two struggle for it and pop, one dead lawyer.
- Amoral Attorney: Andrew King. We don't get a view of any shifty courtroom tactics, but he was willing to hire someone to bump off his mistress when she got knocked up and wouldn't abort.
- Amusing Injuries: Mark spends the episode with his finger in a splint, and he refuses to explain how he got it. At the end of the episode, Mark advises Norman on reaching into a vending machine to get a stuck item out of it, and points to his finger as proof why... and then Norman cries out in pain.
- Asshole Victim:
- Michael Dern was a misogynistic serial killer, so when he gets shived, no-one's sad about it.
- Ditto for Andrew King, who ordered his pregnant mistress dead to avoid her ruining his access to his wife's money.
- A Deadly Affair: Dusty Wohlmann, murdered indirectly on her married lover's order.
- Death of a Child: While we're not certain exactly how far Dusty was into her pregnancy, she definitely was when Dr. Blank killed her.
- Framing the Guilty Party: In order to throw suspicion off himself, Andrew King manipulated Al Blank to murder his mistress in the manner of the Casanova Killer, since as medical examiner he would have all the details that would let him perfectly copy it.
- The Illegible: Dr. Blank has some pretty lousy handwriting, as Mark discovers when reading his notes on the autopsy on the latest victim.Mark: OK, "cause of death: multiple (mumbling) cause by... 'iced puck'". Gotta watch those ice pucks— boy they'll get you.
- I Never Said It Was Poison: Steve and Dr. Blank both talk about how they are keeping certain details about the murder (specifically the "X" carved into the victim's right foot) out of the public ear to insure they get the right man and anyone confessing to the crimes isn't some wacko looking for attention. It also works wonders when it comes to framing Michael for Dusty's death, as Blank has all the right details for the job.
- Improvised Weapon:
- When Michael is preparing Amanda to be his next victim, she tries to reach for a metal nail file, but he catches on and slams his ice pick on the dresser to stop her. Luckily, she is able to reach a bottle of nail polish remover and splash him in the eyes with it.
- It is assumed the Michael himself was stabbed to death with some sort of shiv. The warden says no murder weapon has been found, but most prisoners know how to make a shiv disappear in seconds.
- The Loins Sleep Tonight: Mark eventually deduces that the lack on any sexual contact on the Casanova Killer's victims is due to the fact that he is impotent. When he rubs it into the killer's face on one call, it rattles him enough to let Steve actually trace him.
- Make It Look Like an Accident: Blank's plan when Mark figures him out is to seal him in a corpse locker with some dry ice and water in a bowl. The CO2 fumes released would suffocate Mark, and as CO2 is released in the blood in a natural death, it would just look like Mark had a heart attack.
- Multi-Part Episode: This makes Season four's.
- No-Respect Guy: Albert Blank feels himself to be this, which made it easy for Andrew King to manipulate him into killing his mistress and framing the Casanova Killer for it.
- Noodle Incident: Al got the idea for his dry ice method of murdering Mark from another case he worked on. He even admits that the only reason he even knows the victim even died that way is because the killer confessed to it.
- Red Baron: "The Casanova Killer".
- Serial Killer: Michael "The Casanova Killer" Dern.
- Vanity License Plate: Amanda has one on her car reading "DOCTOR AL". This causes confusion to Mark when the Casanova Killer says he'll kill "Dr. Al" to really get Mark's attention, as he first believes that he's talking about Dr. Blank.
- You Have Outlived Your Usefulness: After getting Bobby Scott to kill Michael Dern, the copycat gets him to overdose on very pure heroin to keep him from talking.
