Hoofbeats on the Trail — Mark Littleton

When a mysterious boy rides out of the woods and into Ally's life, her fun-spirited friend Nick becomes jealous-and suspicious. Who is this bold Jeff Kruck? Why does he live with his aunt but spend so much time in the woods? Why does he sneak around at night? Is Jeff behind a rash of break-ins and vandalism in the neighborhood?
In the quest for answers, Ally learns you can't always paint someone "bad" or "guilty" with a single stroke. As she tries to convince Nick, and herself, that Jeff may not be the neighborhood vandal, she learns deeper issues are at hand. Can she help the truly troubled Jeff and show Nick there's room for many friends in a girl's life? Ally surprises even herself in this third book of the Ally O'Connor Adventures.
About the series: Whether saving wild mustangs at a nature preserve or encouraging teammates to try new moves in gymnastics, Ally O'Connor is a girl with a sense of mission. As she searches to find her own place and purpose in the world, she helps others do the same. Her faith and love of life are contagious, as Nick, his little sister, Molly, and others join in Ally's adventures.