When Denham decides to stay the night at the creepy Fen Inn, he is surprised to find his old friend Francis Briarfield a fellow-guest. He is even more surprised, upon waking the following day, to find the inn deserted and Briarfield murdered. Is Denham mad? Or could the answer to the riddle have something to do with Briarfield's twin brother, Felix..?. The mystery deepens when Denham rushes to inform Briarfield's relatives - only to find his 'dead' friend alive and well.