The Real Ghostbusters S02 E48 Apocalypse -- What, Now?

"Who you gonna call? Ghostbusters!"

The Canon of St Theophilus, a book missing from an abbey in Greece since the 1860s, turns up at a New York auction and is accidentally purchased by Peter. Unbeknownst to the Ghostbusters, the sealed volume contains within it the Four Horsemen of the Apocalypse.