Snoopy receives a mysterious letter that reveals his former owner, Lila, is in the hospital. Compelled by loyalty and concern, Snoopy decides to leave his current home with Charlie Brown to visit Lila. He faces various challenges during his journey, including conflicts with ferocious animals, strict regulations against dogs in certain areas, and even separation from Woodstock. Despite these obstacles, Snoopy remains steadfast in his mission, showcasing his resourcefulness and determination to reunite with Lila, whose need for companionship deeply resonates with him.

Meanwhile, Charlie Brown and the rest of the Peanuts gang feel the sudden void left by Snoopy’s departure. Their attempts to locate and bring Snoopy back reflect their deep bond with the beloved beagle. They struggle to adjust to life without their loyal friend, showcasing the impact Snoopy has on each of their lives. The storyline develops through their honest emotions and genuine longing for his return, thus intertwining Snoopy's adventurous journey with the heartfelt experiences of those he left behind. The narrative beautifully balances themes of friendship, loyalty, and the challenges of letting go while holding onto cherished memories.