A small girl's reaction to the arrival of a baby brother is assumed to be sibling jealousy. No-one is aware that her mother, Susan, has concealed the fact that her own family history contains sinister genes. Gemma's attempts at getting rid of her brother have unexpected results, but as Leo becomes aware of the threat he learns how to evade it. Puberty brings the voices urging Gemma to remove those who threaten her superiority and the Box Day tsunami...