The adorable mouse best friends are back, brainstorming, problem-solving, and celebrating 100 days of school. Miss Maxwell's class pets get in on all the action, writing stories, reporting the weather, and celebrating special days alongside the racially diverse human students. So when the teacher announces a 100th-day party and an assignment to collect and bring in 100 objects, Fergus and Zeke are on it. But do they have 100 of any one thing? Patterning their work on that of their human classmates, they attempt a tower of wood chips…that falls at 47. Zeke's attempt to run 100 miles on their rodent wheel fails: "One hundred is a very big number when you're counting miles." They find the opposite is true when they take a nap of 100 seconds. For their joint 100-word story, author Zeke reaches 100 words just as his character, Fergus, is grabbed by a hungry monster. At the eleventh hour, a misstep by Fergus and some quick thinking by Zeke mean that the two will have a project after all. Messner and Ross again perfectly straddle the line between easy readers and chapter books, with delightful illustrations showing both wide-angle views and the perspective of the tiny mice breaking up the text. (This book was reviewed digitally.) Readers may have to count to 100 to cool their heels waiting for this clever pair's next adventure. (Early reader. 6-9) Copyright (c) Kirkus Reviews, used with permission.