The Elixir of Life — Michael J. Scott

It begins with the abduction of a Holocaust survivor from a New York City mission, but soon escalates as Dr. Jonathan Munro's colleague, Dr. Harry Bryce, an expert in the Middle Ages, is also kidnapped. Jon soon finds himself teamed with his ex-fiancee and artifact-thief, Isabel Kaufman and her new partner: the Irish mercenary Sean MacNeil. Together they work to rescue Harry from an ancient order of alchemists bent on finding The Elixir of Life, a substance thought to cure any disease and prolong life indefinitely. Are they chasing a myth, or is it based on something far more powerful? From Medieval cathedrals to ancient Christian burial sites, pursued by ambitious men who will stop at nothing to possess the prize, Jon must weave back together the diverse threads of Middle Age myths and secret clues to discover the startling tapestry of truth behind them all. Can Jonathan find Harry in time, or will they all be sacrificed to the ambitions of men who would live forever?"