What's the Matter Marlo? is a picture book about best friends that highlights empathy, as well as anger and sadness, and reminds us that these aren't feelings to run away from, but instead to help each other through.

Marlo and Coco are best friends. They do everything together—they read together, laugh together, and play games together. After all, they’re best friends. And that’s what best friends do.

But one day, when Coco asks Marlo to play, he doesn’t answer. Instead, Marlo turns away ignoring Coco, until he’s lost in his anger. Coco is worried about her friend, but then she remembers she can always find Marlo.

In this charming, thoughtful picture book, author-illustrator Andrew Arnold explores empathy and sadness, and how friends can help each other navigate big emotions. Because that’s what best friends do.