It follows a submarine crew that detects a "heat signature" from an enemy, only to realize they cannot find their own signature, suggesting they might be ghosts or in a supernatural situation.
Within the show's universe, Heat Signature is a pre-war film series that Finn and Jake consider a must-watch. Key details include:
The film's tagline is "Under the ocean, no one will hear your death" —a play on the famous Alien tagline.
It is described as a thriller/horror film set underwater.