Abby, Toby, and Billy are ordinary detectives with extraordinary clients: G-G-Ghosts! It's just another summer day of hunting frogs for young Billy, Abby, and Toby, when they stumble upon a deserted lake cabin and meet Mary, a real live ghost (!), searching for her lost locket. The trio offer to help her find it and the Fantastic Phantasmic Detective Agency is launched. But when the agency enlists the help of a grumpy local medium to help them with their second request, locating a ghost's missing ghost brother, a mysterious visitor from the UnderWorld appears. Soon the youthful sleuths are entangled in a conflict between rebellious spirits, undead bounty hunters, officious Bureaucrats from the afterlife, and a very traitorous UnderWorld Demon Ambassador.