Leaving Poppy - Kate Cann

Amber's family think she's gone to Cornwall on holiday, but really
she's left home. She's forging a new life - new housemates, new
job and (with a little luck) new boyfriend. She feels bad because
her mother and Poppy need her, but she's got to make the break,
get out of their clutches...
Then Amber falls ill and her family come to look after her. Something
in the house responds to Poppy's presence, something malign
and threatening. When Poppy moves into the attic, it gets even stronger,
until evil seems to permeate everywhere and Amber thinks
she might never be able to escape...
A chilling and absorbing novel from a brilliant storyteller.