Magnum finds himself locked into a mystery when a bank teller accidentally traps the two of them in a time-release vault at Robin Master's bank. Inside, they find large amounts of counterfeit bills, which the teller believes is proof that her father, a world-famous painting forger, is back in business.

St. Louis gumshoe Luther H. Gillis returns to Hawaii, accompanied by his secretary Blanche, to attend the annual Private Investigators convention, where Luther has been informed he will receive an award. But while Luther and Magnum attend the convention, Higgins and Blanche are kidnapped from the Estate, and the two P.I.'s find themselves having to join forces once again.