The Iron Bells Book I: The Demon's Gate Trilogy

Demons have crossed a gate into our world, taking the reins of power from humanity. A new Inquisition has begun, determined to root out any who stand against the new world order. The holy sites on Earth have been destroyed and what Resistance remains is ruthlessly crushed. Amaranth is a fighter in the Resistance cell based in London. Dham is a ringer, one of the few people left able to ring the remaining sets of blessed hand bells that have power over demons. When Amaranth discovers that her best friend has been possessed by a demon and is going to be used in the Resistance's final desperate mission, she asks Dham for his help in saving her friend.