The popular and Geisel Award–winning mouse sibs (Benny and Penny in the Big No-No!, 2009) meet their greatest challenge yet when hard-playing, toy-breaking cousin Bo saunters over for a visit. Ignoring their efforts to stonewall him, Bo aggressively messes up the sandbox, snatches Benny’s homemade treasure map away and generally makes a nuisance of himself while sneering “Oh, are you going to tell your Mommy?” Eventually the tables turn when Bo needs help getting un-stuck from a hole in the fence, and by the end he shows preliminary signs of acquiring better socialization skills. All three furry playmates sport eloquent eyebrows and other easy-to-spot emotional markers in Hayes’s sunny backyard scenes—and even prereaders may note that when toys get broken here, it’s while Benny or Penny are trying to grab them out of Bo’s hands. A thought-provoking episode just right for the I Can Read set. (Graphic early reader. 5-7)