When the circus comes to the village newly wealthy clown Reggie Smythe reminds waitress Laura Hope, engaged to young Nicholas, that she once promised to marry either him or circus hypnotist Arthur Welkin, whichever made his fortune first. Laura is quick to point out that she was only joking, but then Reggie is found stabbed to death after being threatened by Arthur Welkin--though Welkin has an alibi. Laura amazes everybody by agreeing to marry the hypnotist, so Father Brown announces that he will conduct the ceremony - and so uncover the truth.