Your girlfriend was abducted by Dr. Fred, presumably for some evil experiment. Naturally, you grab two of your friends, and set out to rescue Sandy from the doctor's house -- the Maniac Mansion.
With a plot like this, it can only be a Horror B-movie. Or, since we're no longer in the 1960s, a computer game parody on that genre. LucasArts' adventure game pays homage to a bunch of cliches, spotting a secret lab, tentacles left over from previous experiments, a family on a similar wierdness level as The Addams Family, and a hidden mastermind, whose identity is only gradually revealed.
In Maniac Mansion you find a chainsaw. That looked very helpful for some special problems, but you couldn't find the gasoline. A lot of talk was generated whether there really was gasoline to find anywhere in the adventure. It wasn't.
One author must admit that he played hunt-the-pixel for some hours in the mansion's basement. Rumor had it that there was a miniscule hole in one of the pipes, containing the "hot key", which would unlock a cabinet holding the treasured fuel.
The successor game Zak McCracken had the gasoline, but alas, no chainsaw. For years to come that was an in-joke.
You can also play this game in the sequel Day of the Tentacle, where there is an old computer which runs Maniac Mansion.