When consumptive Doctor Edward Armstrong turns up at Baker Street with an invitation to visit a mysterious Island, Sherlock Holmes smells a rat. Sounding deviously similar to the plot of a recent novel by celebrated lady author Mrs Christie, Holmes decides to send his inveterate side-kick Watson to the island, along with the Doctor’s lovely, but wonky-eyed wife, Mary, and a well-known Scotland Yard detective. Taking Armstrong’s place, the team determine to find out exactly what’s going on, but before they’ve even left the mainland, one of the guests is murdered.