Sam is the grocer who unwittingly becomes Mary’s alibi. After the murder, Mary chats casually and briefly with Sam, giving the impression that she is buying vegetables for her husband’s dinner at Sam’s store. Later, the police confirm her story with the grocer, who, like the detectives, has been deceived by Mary.
The timeline below shows where the character Sam appears in Lamb to the Slaughter. The colored dots and icons indicate which themes are associated with that appearance.
Lamb to the Slaughter
...rehearsed enough, Mary goes outside to a grocery shop and chats briefly and casually with Sam, the grocer, pretending that she is gathering food for her husband’s dinner and speaking about... (full context)