This Dark Road to Mercy by Wiley Cash
After their mother's unexpected death, twelve-year-old Easter and her six-year-old sister Ruby are adjusting to life in foster care when their errant father, Wade, suddenly appears. Since Wade signed away his legal rights, the only way he can get his daughters back is to steal them away in the night. Brady Weller, the girls' court-appointed guardian, begins looking for Wade, and he quickly turns up unsettling information linking Wade to a recent armored car heist, one with a whopping $14.5 million missing. But Brady Weller isn't the only one hunting the desperate father. Robert Pruitt, a shady and mercurial man nursing a years-old vendetta, is also determined to find Wade and claim his due.