Professor Charles Grimaud - wealthy, respectable, distinguished - is found dying in his study of a gunshot wound to the chest. His brother Pierre - an ex-con and struggling music-hall magician - had publicly threatened Grimaud's life.

When the police go to pick up Pierre he is lying dead in the street, killed by an unseen assassin. There are a dozen witnesses to both murders, but it takes Dr Fell and the church bells of London to solve the puzzle.