This is the last edition of Saturday night’s The Essentials series on TCM in which Alec Baldwin’s co-host is former 30 Rock co-star Tina Fey. Next week, William Friedkin takes over. But for now, Fey and Baldwin end their summer run by presenting a perfect movie musical: 1952’s Singin’ in the Rain, a joyous depiction of Hollywood during the transition from silent movies to the sound era. Gene Kelly, Donald O’Connor, and a young ingénue named Debbie Reynolds star.