The Time Trap Series Series by Sean Dalton

A member of the twenty-sixth-century's Time Institute, Noel Kedran finds himself transported to, then trapped in, fourteenth-century Greece, where a strange double works to keep him.

A saboteur has duplicated Noel Kedran, a top operative of the Time Institute, and left his twin behind in the past. The twin is his evil self, a dark and twisted offspring of Noel's personality named Leon. Now Noel must track Leon down through the squalid streets and royal palaces of Restoration England.