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. The mystery deepens when Denham rushes to inform Briarfield's relatives - only to find his 'dead' friend alive and well. Is Denham mad? Or could the answer to the riddle have something to do with Briarfield's twin brother, Felix..?