A Jack Russell Terrier named Max lives with his owner Katie in a Manhattan apartment. While she is at work during the day, he hangs out with other pets in the building: tabby cat Chloe, pug Mel, dachshund Buddy, and budgerigar Sweetpea. One day, Katie adopts Duke, a large and shaggy dog from the pound, leaving Max jealous because of her larger focus on Duke. Enraged by Max’s attitude towards him, Duke tries to abandon Max in an alley, but they are both attacked by a gang of alley cats led by Sphynx cat Ozone. The cats remove both dogs’ collars and leave them to be caught by Animal Control. Duke fears that he will be put down if he goes back to the pound.