Snoopy Come Home (1972)

With his avian friend Woodstock by his side, independently-minded Snoopy heads off after he receives a letter from someone named Lila who mentions that she would like him to come visit her as she has been hospitalized. Not knowing who Lila is, Charlie Brown and his friends each believe that Snoopy left as he has been unhappy in a disagreement with many of them. Regardless, Charlie Brown is determined to find out who Lila is and to do whatever required to get Snoopy back home. If Charlie Brown discovers the truth, he will indeed discover that Snoopy has been increasingly unhappy, more so in that many of the places he likes to frequent have become "no dogs allowed", but his hasty departure is more to comfort a friend in need, Lila his owner before she had to give him up, then when he was sent to the Daisy Hill Puppy Farm for adoption. Beyond Snoopy and Woodstock's misadventures en route to the hospital, Snoopy will have to figure out where his allegiances and heart lie when Lila tells him that, upon her imminent release from the hospital, she'd like him back for good.