The Alchemist's Secret (Ben Hope #1) by Scott Mariani

Ben Hope, a former elite SAS soldier tortured by a tragedy from his past, who now devotes his life to rescuing kidnapped children.

But when Ben is recruited to locate an ancient manuscript which could save a dying child, he embarks on the deadliest quest of his life.

The document is alleged to contain the formula for the elixir of life, discovered by the brilliant alchemist Fulcanelli decades before. But it soon becomes apparent that others are hunting this most precious of treasures – for far more evil ends. It seems that everyone – from the Nazis of the past to the shadowy modern organization known as Gladius Domini – wants to uncover the secrets of immortality.

Teaming up with attractive American scientist Dr. Roberta Ryder, Ben is led on a wild and dangerous trail from Paris to the ancient Cathar strongholds of the Languedoc, where an astonishing secret has lain hidden for centuries.