This is one of those picture books where illustrations and prose are in a symbiotic relationship. They complement and rely on one another. The pictures are more meaningful with the words, and the words make more sense with the pictures. Corinna uses a palette of reds and blues to, at first, differentiate the boy and girl, and then meld them into purples as they come together. She captures the old man's sadness over his lost dog with a hunched silhouette. Kate employs repetition - "nothing in common" - to emphasize her theme, and surprises readers with quiet, quirky, philosophical word choices: "They looked on the same quiet rooftops, and under the same whale, and near the same planets." Gentle humor rises from the lost dog in the balloon, and empathy descends as they work together to bring the dog home to his elder companion. The end circles back to the beginning - my favorite story round. ( )