This book started off slow but then became very intriguing, creepy and gripping. It tells the story of Alfie, whose wife (Pippa) had recently died after an accident, his twin daughters and Julia, Pippa's twin sister. It is told through two different perspectives - Alfie and Julia. When the twin daughters, Sylvie and Cassia, begin to see Black Mamba and start to misbehave, Alfie and Julia are not sure if he is an 'imaginary friend' which the twins are using as a coping mechanism in their grief or is something more sinister like a demon. The story quickly becomes darker and also explores the lives of Pippa and Julia growing up and as well as grief and difficulties within family relationships as they try to find out the truth. The story is creepy and full of suspense and a lot is left to the imagination of the reader. It is well worth a read if you like horror psychological thrillers.