Sisters Megan and Ffion have never had secrets, so when Megan goes to flat-sit all she's expecting is a rest and a change.
When a stranger called Jack phones, Megan wonders who he is. Ffion behaves like she's just seen a ghost, and refuses to say any more.
So is Jack a ghost?
Ffion's not telling and when she disappears too, the mystery deepens. Megan begins to fear for the future. She's always been the one who's looked after her little sister.
Is this going to be the one time she can't?