Benji, a stray dog who lives in an abandoned house on the outskirts of a small town, sets about his daily ritual of visiting human friends; he has no fixed home but he desires one, and he likes the children of the Chapman family, Paul and Cindy, best. Mary, their housekeeper, feeds him, but she knows that the children’s father, Dr. Chapman, must not find out about him because he’ll fire her on the spot. One day their father is about to appear, so they hide Benji under the table. After outwitting Dr. Chapman, the children leave for school and Mary explains to Benji that Dr. Chapman stubbornly dislikes dogs, but he is a nice man. Continuing on his route, Benji chases a cat and greets Officer Tuttle, who announces his wedding engagement and tells Benji that he, too, will soon meet the lady of his dreams. At Bill’s Café, Benji wakes Bill from his morning nap and receives a bone as payment. Returning home, Benji finds three suspicious characters, Linda, Henry, and Riley, breaking in. Although Henry and Riley are spooked by legends that the house is haunted, Linda intends to propose the location as a hideout to their boss Mitch, mastermind of their illicit activities. Henry leaves a bag of groceries behind and Benji eagerly consumes an open pudding cup.
The next morning at the Chapman home, the children brush Benji, hoping their father will accept him into the family, but Mary tells them that the doctor will not change his mind. After impressing his human friends with his new hairstyle, Benji encounters a pretty white dog in the park who is scavenging through his favorite trashcan. Benji presents her with the bone he received from Bill and she follows him back to the Chapman house where Mary brushes her, brings her food and names her Tiffany after the jewelry store. Benji and Tiffany frolic in the park, but when they return to Benji’s home, they find that Riley and Henry have returned. Riley points out that Henry’s groceries have been overturned and becomes increasingly anxious that the house is haunted. As Mitch and Linda arrive to survey the property, Riley tells Henry that a pudding cup is missing, but Henry warns him against upsetting their plans.
The following morning, Dr. Chapman tells his despondent children that Benji carries diseases and forbids them from keeping him as a pet in spite of Cindy’s tearful pleas. Later, Riley writes a ransom note to extort money from Dr. Chapman by threatening his children, but Henry throws it on the ground, writes a new one, and orders Riley to deliver it when he gives him the signal. Meanwhile, Mitch surprises Henry and Linda by actually kidnapping the Chapman children. Benji races to the Chapman home to alert the humans but is shooed out by Mary, not understanding his message. Benji returns to steal the ransom note, hoping that by doing that, he’ll make the police follow him to the source of trouble, but he is stopped and the note is taken from him. Benji is at a loss at what to do next. He then follows Officer Tuttle into the police station but gets locked in. When he barks through an intercom, he is released by a passing policeman.
Returning to the crime scene, he snatches Riley’s first ransom note and is grabbed by Mitch. Tiffany rushes out and bites him and gets a vicious kick in return; she is not killed, but her leg is sore and bruised. Benji runs home where he finds that Linda has preceded him in an attempt to cut off his efforts. She snatches the note from Benji and puts it in her purse. He growls and barks, and Mary berates him and carries him away, but he bites her and lunges at Linda, causing the note to fall out. Mary reads it and rushes it to Dr. Chapman, who demands to know where his children are, and Linda breaks down in tears. Benji leads the police, the FBI, Dr. Chapman, and Mary back to the hideout. Meanwhile, the kidnappers are concerned that Linda has not returned, and Henry and Riley argue that they should leave. As they walk outside, however, the police hold them at gunpoint and the children are reunited with their father and Mary. Their father is so proud of the dogs that he says they can stay with them permanently, much to their and the children’s delight.