Yvonne Erwin guests as Clair's sister Sarah, who shows up at the Huxtables to announce her engagement. Helpfully, Clair (Phylicia Rashad) and her mother Carrie (Ethel Ayler) volunteer to give Sarah sage advice on married life. Before long, all three women are laughing hysterically--and Cliff (Bill Cosby) is not only annoyed by this, but also by the fact that they abruptly stop laughing the minute he enters the room! Elsewhere, Cliff struggles manfully to beat his father-in-law (played by singer Joe Williams) at chess. A young Mario Van Peebles appears in this episode, which is highlighted by Joe Williams and Phylicia Rashad's soulful rendition of "We Belong Together". ~ Hal Erickson, Rovi