Alistair Sim plays a mild, innocuous little watchmaker who spends his off-hours as a professional assassin. His present target is windbag cabinet member
Raymond Huntley. After various misfire attempts, Sim plants a bomb in a small radio and waits for the tube to warm up--but the authorities by now are on to him. The Green Man has some excellent setpieces, notably a droll snatch of black humor involving a body stuffed in a piano. The film's only debit is that, in the play upon which it is based, Frank Launder and Sidney Gilliat's Meet the Body, Sim's character is secondary, almost peripheral. By reshaping the film into a star vehicle, much of the play's intimate (albeit ghoulish) charm is dissipated. ~ Hal Erickson, All Movie Guide