By the Sword - F Paul Wilson

Jack is hired to find a legendary Japanese sword, a katana stolen from the Hiroshima Peace Museum and brought to New York City. To get it back, he maneuvers his rivals for possession of the sword--the members of a weird Japanese cult, a young Japanese businessman and his three Yakuza bodyguards, and Kicker Cult leader Hank Thompson--into a bloody melee from which Jack plans to waltz away with the fabled artifact.

Also in the mix is a pregnant teenager whose unborn child, loaded with abnormal DNA, will be a decisive force in the cosmic shadow war raging behind the scenes. A pawn in the game, she is hunted by both sides.

Of course, when things don't go as planned, Jack must improvise (and he hates to improvise).