The Sweathogs formed a singing group. They called themselves Three Do's and a Don't. The guys put on matching bedazzled denim outfits for a city talent contest in season three of Welcome Back, Kotter. Things are going swell for Barbarino, Horshack, Epstein and Washington… until Barbarino falls for Cassy, a blonde competitor.

This love affair happened in "Barbarino in Love," in the fall of 1977. The two-part episode aired just weeks before Saturday Night Fever hit theaters. Naturally, John Travolta was given the opportunity to sing and dance. Travolta even does the iconic "V across the eyes" move when dancing that he would do in Pulp Fiction decades later. But Barbarino's love threatens to upend Three Do's and a Don't. Vinnie briefly quits the group, unwilling to compete against his crush.

Playing Cassy was Amy Johnston, who was making her screen debut with this sitcom. She used her singing skills to land guest roles on television. Two years later, she popped up on Charlie's Angels in "Angels on the Street," singing a tune called "If I Could See" in the opening scene.

That same year, Johnston landed a lead role in Brothers and Sister, a sitcom about frats and sororities that was blatantly capitalizing on the popularity of Animal House. She played a snobby sister named Mary Lee, who in one episode must babysit a chimpanzee. The series, which premiered following the Super Bowl, lasted one season.

Everett CollectionJohnston in 'Brothers and Sisters'

Johnston played an entirely different sort of sister in Sister Terri, a 1978 pilot that paired her with Pam Dawber (Mork & Mindy). That show was not picked up. 

Nevertheless, her career peaked that year, when Johnston played Cindy Lou, the first love of Buddy Holly (Gary Busey) in The Buddy Holly Story. Her character was the inspiration behind his song "Cindy Lou," which eventually became "Peggy Sue."

Her Hollywood career dried up in the 1980s, outside of a couple of guest appearances on Highway to Heaven and Cagney & Lacey. Later, she lived in Arkansas, where she taught drama. On March 17, she died in her West Fork, Arkansas, home according to The Hollywood Reporter. She was 66.