Five years after the events of Maniac Mansion, Purple Tentacle—a mutant monster and lab assistant created by mad scientist Dr. Fred Edison—drinks toxic sludge from Dr. Fred's laboratory. The sludge causes him to grow a pair of flipper-like arms and develop a vastly increased intelligence and a thirst for global domination. Dr. Fred plans to resolve the issue by killing Purple Tentacle and his harmless, friendly brother Green Tentacle, but before he can Green Tentacle sends a plea of help to his old friend, the nerd Bernard Bernoulli. Bernard travels to the Edison family motel with his two housemates, deranged medical student Laverne and roadie Hoagie, and frees the tentacles. Purple Tentacle escapes to resume his quest to take over the world.