Two kids approach an old manor where they are greeted by two old ladies, Georgia and Virginia Bolton, who tell them the tale of how 150 years ago in a nearby swamp, a monster rose from the mud and headed into Gotham City to terrorize the city's architects. They warn that with the lunar eclipse Grundy will rise again, and that they're the granddaughters of one of his victims. The kids run away in terror and afterward they toast their grandfather, who left them money. But they're interrupted by echoing footsteps and a huge figure comes crashing into the house.
Later at Wayne Manor Alfred is greeted by trick-or-treaters, including one dressed as Grundy. They're interrupted by the Bat-Wave, and Bruce dons the uniform to go the manor and visit the granddaughters. The manor is wrecked and they warn that Solomon Grundy came for them, and will go for the others. Batman follows the path of destruction to another of the descendents and finds Grundy attacking Winslow. While Winslow runs, Grundy attacks Batman and readily overpowers him then leaves, destroying the house.
The Batman vs. "Solomon Grundy"
Bruce returns to Wayne Manor and notices Alfred reading a book on the zombie. The book reveals the swamp was once a lake and a home to Eastern European immigrants. But three rich businessmen (Bolton, Winslow, and Parish) contaminated the area, turning it into a dumping ground of industrial waste and turning it into a swamp. The laborers used magic and summoned the zombie to haunt the businessmen and their ancestors.
Bruce takes a sample of the mud from Grundy for analysis and then takes off for the ancestor of the third industrialist, Parish, a wax museum owner. Batman gets a message from Alfred confirming the analysis – the mud itself has traces of DNA in it and then Grundy attacks.
The two fight but Batman knocks a piece of "Grundy" loose, and he's revealed as …Clayface. He's after the descendants' money, using "Grundy" as a cover. Reverting to shape shifting, Clayface flees into the wax museum and Batman goes after him. Disguised as an alien statue, Clayface attacks and Batman partially freezes him before Clayface sends him flying. He escapes but Batman follows a trace of clay stuck in the mud into Parish's office and the vault where he keeps his money. Inside the vault door is…a vault door – Clayface is disguised as the first vault door. Clayface embraces Batman who uses a taser to drive him off but is knocked into the wax factory. Clayface tires to knock him into the hot wax but he gets free and when Clayface fires arrows at him, he knocks the vault of hot wax onto himself, locking him in the substance. Later, Alfred calls an end to Halloween but is skeptical as to whether they've "proven" Grundy doesn't exist. Down at the swamps, the two kids from the beginning leave the swamp but hear a moaning noise as a figure starts to emerge. - TV.COM