We begin with a private eye narrating about different buildings that have changed, including the firehouse. Then, a ghost rises from the ground, disturbing some construction workers. The Ghostbusters (with Ray eager but Peter feeling a bit lazy and wanting the day off) attack it, but it curses some vehicles and has them chase the Ghostbusters. They split up for no reason (Peter with Ray and Winston with Egon) and then the ghost escapes. Peter and Ray are cornered by a cursed excavator, but it stops once the ghost is back underground. Winston and Egon then catch up with them on the nearby wall.
The private eye narrates that he is after the ghost, whose name is Blackey, and it is subsequently revealed that he's a ghost too. He enters the firehouse, while the Ghostbusters are trying to track Blackey with a map, and bumps into Slimer, scaring him. When Peter leaves to change out of his slime-soaked uniform (because Slimer hugged him), the ghost detective opens the window, blowing newspapers around, then leaves a relevant newspaper on the table. The newspaper has an article about who the detective was in life, revealing his name to be Philip Spade.
Philip Spade then enters the kitchen (where Peter is looking for food) and gives him a history book. Peter shows the guys the book, which has an illustration of what Blackey was before he died, and the four of them go down the hole to catch Blackey. After a bit of poking around, they find him. He attacks them and is about to kill Peter, but is stopped by Philip Spade.
The Ghostbusters run away and back at the firehouse, Philip Spade reappears and explains that in life, Blackey was a thief, and that he died of a curse that made him obsessively guard the treasure he stole. Thus, the Ghostbusters and Spade decide to head down to the sewer, find the treasure, and return it to break the curse. However, Spade disappears and Blackey appears. After they find the hole the treasure is in, Spade reappears and puts his hands over Blackey's eyes, while Egon and Winston retrieve the treasure. They drive to the museum (with Blackey in pursuit) and return the treasure, breaking the curse. This causes Blackey and Spade to disappear into the afterlife.
This episode provides examples of
- Absurdly Spacious Sewer: The abandoned sewer where Blackey resides is very large and roomy.
- Covered in Gunge: Slimer gets ectoplasm on Peter when he hugs him.
- Dark Is Evil: Blackey is a homicidal, cursed ghost with dark grey skin.
- Dead All Along: It's not until about halfway in that Philip is revealed to be a ghost.
- Everyone Has Standards: Philip Spade dislikes the Ghostbusters, but doesn't feel they deserve death.
- Hurricane of Euphemisms: After explaining that he's a private eye, Philip Spade lists synonyms for "private eye".
- Private Eye Monologue: Philip speaks like this for much of the episode.
- Pun: Winston claims that Egon is "just hanging out" when Egon is literally hanging, as in suspended, by his proton pack.
- Red Eyes, Take Warning: Blackey has red eyes and tries to kill people.
- Swiper, No Swiping!: Discussed when Peter tells Spade to do something about Blackey, and Spade replies, "What am I gonna do? Ask him to stop it?!".
