'The Captive Soul' by Josepha Sherman

There can be only one...

He is Immortal. A Scottish warrior born four hundred years ago. He is not alone. For centuries he has fought others like himself. He can die only if a foe takes his head, capturing his life-force in an event known as the Quickening. But his battles are eternal...for in the end, there can be only one. He is Duncan MacLeod. The Highlander.

An Ancient Evil...

Over three thousand years ago, Methos helped the Egyptian pharaohs in their battle against sadistic Hyksos overlords. Then he fought Khyan, an Immortal Hyksos prince, but failed to take his head. Now a deadly madman stalks modern New York City, hunting an ancient sword, killing all who stand in his way. It can only be Khyan, seeking revenge. If Methos does not destroy this darkness from his past, he, Duncan MacLeod, and indeed all Immortals will be doomed...

Notes:
*Featuring Duncan MacLeod