The Watchers (The Angelus Trilogy #01)

Every hour, childlike Marc Rochat circles the Lausanne cathedral as the watchmen have done for centuries. Then one day a beautiful woman draws him out of the shadows - the angel his mother once promised him would come. But Katherine Taylor is no angel. She's one of the toughest and most resourceful call girls in Lausanne. Until something unnatural seething beneath a new client's request sends her fleeing to the sanctuary of an unlikely protector. Into their refuge comes Jay Harper. The private detective has awakened in Lausanne with no memory of how he got there - and only one thing driving him forward: a series of unsettling murders he feels compelled to solve.