The ghost chasers agree to take some publicity photos of the Partridge kids on The Sea Witch, a haunted pirate ship, but soon they all find themselves adrift and at the mercy of twin ghosts, one good and one evil.
The ghost chasers head to England and team with Detective Sergeant Roger Sherlock to investigate thefts at Blimey Mansion, which is haunted by numerous ghosts.
Gilly's Aunt Wilma sends for the ghost chasers to join her in the South American jungle to see the ghost of an ancient Inca chief who guards a lost city.