A pampered Jack Russell Terrier named Max lives with his owner Katie in a Manhattan apartment. While Katie is at work during the day, Max hangs out with other pets in the building: tabby cat Chloe, pug Mel, dachshund Buddy, and budgerigar Sweet Pea. One day, Katie adopts Duke, a large Newfoundland mix from the pound, leaving Max jealous because of her divided focus on Duke. Enraged by Max's attitude towards him, Duke tries to abandon Max in an alley, but they are both attacked by cats led by Sphynx cat Ozone who steals both dogs' collars and leaves them to be caught by Animal Control. Duke fears that he will be killed if he goes back to the pound. When Gidget, a white Pomeranian who has a crush on Max, discovers that he is missing, she decides to find him.