Before the Flood. The Seraph Chronicles, #5

The year is 2034 and Britain is a drowning isle, after a cataclysmic wave destroyed her cities, killing millions, raising the sea level by 60 metres and changing the landscape forever. The Flood has brought Albion to her knees and now the Devils, a race of malevolent sea creatures, haunt her coasts as the survivors retreat inland, struggling for their very existence. Mankind learns to fear the sea and avoid the water.
When a mysterious island surfaces off the coast of Wales, a small team of British militia under the command of the war weary veteran Sergeant Emma Stokes, is dispatched to investigate this new threat. But a chance meeting with the mysterious Major Seraph takes them on a dangerous odyssey through this drowned world, to the hidden fortress-city of Gwaelod, which seems to offer new hope in the battle against the creatures.
Yet as humanity clutches on by its fingertips, who are the real enemies in this deadly flooded world?