Lost Bullet — Malcolm Rose

Recently qualified as a forensic investigator, Luke Harding is assigned to the slums of London, where he and Malc investigate a doctor's murder. They find a bullet wound to her head, but rain has washed away the bullet -- and all other clues. As more innocent doctors die, Luke's sleuthing leads him to a mysterious cult called The Visionaries. With no time to lose, Luke must infiltrate the sect and find the culprit before the bizarre shooting spree becomes an all-out massacre.