Mr. Ludgrove is killed by two of his guests. The murder is in full view of the audience. In consequence of the carefully prepared alibi that each of the assassins is able to establish, the official examination into the cause of Ludgrove's death establishes a clear case of suicide. But in the house is a charming young sleuth-hound in the person of Susan Cunningham, who had beguiled the time between house parties with mystery stories. Susan becomes suspicious, and sets out to find the murderer. The discovery that the blotting paper had been removed from the pad and an infinitesimal flaw in the alibi, incriminate the men.