What hypothetical question does Ms. Hussey ask the Calder and Petra and what is their response?

Ms. Hussey asks Calder and Petra to think of how they would react if the thief had given them a letter asking them to help steal the painting and to not show the letter to anyone. Ms. Hussey gets upset while discussing what they might do. Calder and Petra worry about her and her involvement in the crime.