The Centurion's Son — Lynne Benton

The book is set in Roman Britain in the year 312 AD. When 12-year-old Felix's father, Gaius, the Senior Centurion in the Second Augustan Legion, disappears and is then accused of disgracing the Legion, Felix knows it can't be true. He then learns that he himself is to be sold as a slave in punishment for his father's supposed crime. With the help of his slave friend Catrin he manages to evade capture, and the pair determine to find out what has happened to Gaius. Why has the whole Legion turned against him? Can Catrin's second sight lead them to the truth? And can they find out before Felix is recaptured?