The Devil's Architect - The Dark Horizon Trilogy, #2

Driven by unearthly visions, a convicted killer escapes from a maximum-security psychiatric hospital. Days later a woman is ritualistically murdered in the grounds of a mysterious London church. When a Roman coin is discovered under the victim's skin, Vincent Blake - London's leading stolen-art investigator - is called in to assist the police with their investigations. A series of copycat murders, all carried out within the vicinity of connected London churches rocks the heart of the city.
As the body count rises, Blake is thrust into a race against time to solve a centuries-old mystery that sets him on a collision course with a terrifying secret. Nothing can prepare him for what he has to face, because the churches are not what they seem . they have been designed by the Devil's Architect.