Clair agrees to let Cliff have some friends over to celebrate his 50th birthday. She bristles at his desire to invite his friend Mark, who was once married to a good friend of Clair's, but decides that she can tolerate him for one night. Cliff has a birthday lunch with the kids, who then "honor" him with a presentation entitled "Things That Are Older Than Dad." They also give him a key ring that beeps at the sound of clapping, but he is the only one who cannot get it to work. Mark brings his 12-year-old daughter Ellen to the party because her mother is ill. The girls are at the movies, so Cliff tries to convince Theo to hang out with Ellen. He suggests that Theo be nice to Ellen now so that she will remember him after she grows up to be a gorgeous woman. Theo is unsure, but finds that she is a cool person and asks her to come skating with his friends. Clair behaves coldly toward Mark. After Cliff explains the situation, Mark has a talk with Clair. He says that he is very sorry for cheating on his wife, and will always have to live with the regret of losing her. However, they are now good friends. He asks Clair to give him a chance. She agrees to let him get together with Cliff.