Complex sentence: With no one left to ask, the boys ask Stan's sister, Shelley, to defend them; she agrees, on the condition that they first tell Miss Claridge that they are the ones truly responsible for her disability.
Split into simpler sentences: With no one left to ask, the boys ask Stan's sister, Shelley, to defend them. She agrees, on the condition that they first tell Miss Claridge that they are the ones truly responsible for her disability.