Poopy Pants is Missing Book One. The Von Tripp Triplets book series connects the reader with triplets Rylee, Mylee and Kylee, as well as their beloved horses.In the first book in the series, Poopy Pants is Missing, we meet a funny and talkative girl named Rylee, who can be somewhat mean but still has lots of friends because of her outgoing personality. She gets a horse for her birthday, but she does not take on the responsibility of caring for the horse, who eventually goes missing.Does she find the horse?