The tale of the stalking shadow - David Cody

Rumours about a ghost aren't going to stop Hadley Heering from working at Mrs Vailmon's mansion. The old lady needs a companion, and besides, Hadley is too sendible to believe in ghosts.
Luckily, she's also too smart to deny the truth. Because there is something in the mansion - something dark and evil - that only Hadley and the old woman can see, and it's growing stronger every day. Strong enough to follow Hadley home. Strong enough to threaten her friends. Unless Hadley can unlock its terrible secret, this won't just be her first job - it'll be her last.