Metaphorically, ‘leading a lamb to the slaughter’ means guiding someone, often unknowingly, into a dangerous or harmful situation. The phrase suggests innocence on the part of the person being led, much like a lamb, and a sense of betrayal or manipulation by the one doing the leading.
In the story Lamb to the Slaughter by Roald Dahl, the ‘lamb’ being led to the slaughter is Patrick Maloney. He is unaware of the danger he is in, much like a lamb. The one leading him to the slaughter is his wife, Mary Maloney. She manipulates the situation and Patrick’s trust, ultimately leading to his demise.