Peter's scheming dad is back with a plan to get rich by finding a treasure in Mexico. The others take a pass, but Ray and Slimer join him on the exciting and dangerous adventure.
After getting yelled at by Peter for causing too many interruptions, Slimer has to contend with the ever persistent Professor Dweeb by himself. Meanwhile, the Ghostbusters have to deal with a squid ghost created by the anger of the ghosts in the containment unit.
The Ghostbusters and Slimer arrive in Tokyo, Japan to battle ghosts that resemble Japanese movie monsters.