"Marco Polo is a retired Christmas ornament, but in his mind he is a great mouse explorer. Because he's tiny and likely to be lost, he is the least-borrowed of the Book Buddies--toys that children can check out of the library just like a book--and he almost never leaves the library. But the little mouse finally meets the right match in Seth, a boy who is about to attend his first sleepover. If Seth were to bring the stuffed bunny he usually sleeps...

Roger the chick almost never gets the chance to do things on his own--he's always attached by Velcro to his mother, Olive the hen, who prefers a quiet nap to any excitement. The two Book Buddies even come as a pair when they're borrowed from the library, so Roger doesn't go on many solo adventures. One day, a boy named Liam is persuaded by his little sister to borrow Roger and Olive before picking up Grandpa from the airport. While Liam is preoccupied...