"What are we going to do?" Paul asks, rising up on one elbow to look down at his sister's beautiful face. "We have added adultery to our sin of incest."

"Is it still adultery if Tim knows what we're doing here today?" Sharon asks her brother.

"What are you talking about?" Paul demands.

"He overheard us yesterday when he came back for the sunscreen," she says and then proceeds to tell Paul about the rest of her conversation with Tim, including his research into incest penance and his suggestion that she and Paul have unfinished business.

"Unfinished business," Paul muses. "That's a weird way of referring to it, but I...