When a family brings home Rex from the dog shelter, Moxie isn’t too pleased.

On the surface, the older Moxie and the younger Rex seem cordial in their letters to each other. However, a closer look reveals their true feelings . . .

Rex is excited to belong to a new, loving family, after being adopted from the dog shelter. He’s not the only dog in his new home, though, as he is introduced to the family’s other dog, Moxie.

Rex starts writing letters to Moxie, complimenting her on her quickness getting treats and how shiny her coat is from eating all those treats, and even suggesting she be more comfortable in a larger pillow. As the letters become more frequent, Moxie becomes more suspicious of the true intentions of the letters. Soon, she decides that Rex doesn’t belong in the home any longer, so she becomes determined to get rid of the younger Rex. Will Moxie’s letters to Rex rid her of this nuisance, or will the appearance of an arch enemy, a CAT, finally unite them?