Peter Stirling (Donald O'Connor) is a young and anxious soldier during World War II, who happens to make a special bond with a talking army mule named Francis (Chill Wills). Peter who is the Second Lieutenant in his team is stationed in Burma where he is separated from his team during a battle with the Japanese. While he is wounded in the leg, as well as terrified and exhausted, he is rescued by an unexpected old mule in which the animal brought Peter to safety. However, when Peter tells others about the mule's extraordinary abilities to others, he is seen as lunatic and finds himself ending up in a psychiatric ward where he under the care of Nurse Humpert (Zasu Pitts). During his stay at the ward, a beautiful young refugee named Maureen Gelder (Patricia Medina) caught Peter's eyes. However, what Peter does not know is,she is there as a spy.