An eccentric millionaire, Cadmus Cole, visits the newly founded offices of "Ellery Queen, Confidential Investigations", in a rare incidence of disembarkation from his yacht.

The investigation company is actually the brainchild and sole responsibility of Ellery's partner, "Beau" Rummell, an established private eye.

Rummell, in the guise of Ellery Queen, begins to investigate both the circumstances of Cole's death and his heirs; he soon meets two beautiful young women and the case becomes complicated by romance and the appearance of a claimant under the will.

When the claimant is murdered, and Rummell married to one of the beauties, the real Ellery Queen must take a hand and solve the case, using the vital clue of the chewed fountain pen.

According to critics Barzun and Taylor: "Ellery directs his partner in a vague investigation of a recluse millionaire's death at sea.