Hunting Pearl — C.J. Petit

Will noticed that the numbers didn't add up when he was eleven but didn't discover the truth of that mathematical problem until he was seventeen. For most of his young life, Will had known Pearl as his older sister, but only after the man who had acted as his father died, did he learn that she was really his mother.
Now, despite his youth and lack of experience, he was going to set out on an almost impossible quest to find his mother after more than twelve years. But even as he rode out of San Miguel, he had no idea just how long and dangerous that search would be.