The Shaft by Angus Silvie

When Trey and Lauren moved into their ground floor apartment in Ridley Manor, nothing could have prepared them for what they would find under a locked trapdoor in their basement, or for the nightmare that was about to engulf them. It started with a homeless lady being dragged to her death in nearby woods, but is this connected to the strange opening in their cellar and what lies below? As the death toll rises, the police and a secret Home Office team struggle to deal with a situation none of them has encountered before.

The young couple's world seems about to collapse, and soon they are faced with an impossible dilemma - would you kill a neighbour to save your partner from a life in jail?