The Late Show (1977)

Private detective Ira Wells (Art Carney) isn't getting any younger. He's also barely staying in business. So when Ira's former partner, Harry, is killed, Ira vows to not only take on Harry's last job, but also find his friend's murderer. While trying to crack Harry's case, Ira is introduced to Margo (Lily Tomlin), an eccentric pot-selling agent who wants to hire him to find her cat. Desperate for the work, Ira takes on the pet search and winds up with an unexpected new partner in Margo.