Arthur Bishop is a 'mechanic' - an elite assassin with a strict code requiring professional perfection and total detachment. One of an elite group of assassins, Bishop may be the best in the business - with a unique talent for cleanly eliminating targets. When Harry McKenna, his close friend and mentor, is murdered, Harry's son comes to him with vengeance in his heart and a desire to learn Bishop's trade, signaling the birth of a deadly partnership.

A 14th century Crusader returns with his comrade to a homeland devastated by the Black Plague. The Church commands the two knights to transport a witch to a remote abbey, where monks will perform a ritual in hopes of ending the pestilence.