After a long and stressful week, capped by a thunderstorm and attracting the unwanted attention of a man in a bar, Samantha is too strung up to take Imogen, her younger sister, cycling. So she does the next best thing: she makes a promise to do it next weekend instead.
As the weeks pass, though, Samantha’s promise fails to materialise, slipping further and further away until she has almost forgotten about it. After all, there’s always next week – and Imogen can go alone if she’s that desperate.
But unbeknownst to Samantha, next week might never come. Because there’s something very, very wrong with Imogen – and the ten-year-old’s time is quickly running out.