Sarah is captured by deserters and held for ransom along with two other French ladies and Lady Farthingdale. Her husband genuinely loves her, and is the French envoy bringing ransom to the deserter army of Pot-au-Feu just as Sharpe is the British envoy.
Quick thinking and well educated, she alerts Sharpe as to where she is being held by means of reciting a poem which Sharpe dutifully reports. Nairn then supplies the probable location from the context of the poem. She is subsequently rescued and restored to her husband.