It's 1986 and Halley's Comet is hurtling towards Earth. Everyone is talking about what the comet will bring - wishes could be granted, people might go mad, great disasters could happen... When Andrew is asked to write down his greatest wish for the Comet Box, he can think of only one thing – that his runaway sister Amelia will finally come home. As the comet draws nearer he begins to learn the reasons why she left in the first place and the more he learns, the more he wants to forget. When Amelia is captured and brought home she reveals a shocking secret that makes Andrew's once safe world begin to unravel. As the comet arrives, Andrew must choose whether to be blind to the mistakes of the people around him or to side with his sister as she tears his family apart.