Thanks to my library, I am enjoying Roderick Alleyn stories again. This is a favorite series. Troy has the impulse to take a river cruise. At one stop she explains ” There is a clutch of Constables!”. There a dead silent on the vessel as passengers look for policemen on shore. There are other unusual happenings that bother Troy and she writes to Alleyn about them. Alleyn is looking for a theif and serial murderer A passenger on the boat disappears at night. Later Troy sees the body in the river. Is the killer a passenger on the boat and can Alleyn find him before he escapes again.