As the worst storm of the century breaks across the North West, sweeping through Snowdonia and across the Mersey to burst upon Liverpool, two women. Molly and Ellen, give birth to girls in a Liverpool maternity hospital. Despite their different backgrounds, they become firm friends. Molly lives on a hill farm in Snowdonia while Ellen is married to Sam O'Mara, a dock worker who is quicker with a punch than a kiss. After one punch too many, Ellen throws her husband out, and eventually leaves Liverpool to live with Molly in Snowdonia. Ellen and her daughter throw themselves into their new life with enthusiasm, unaware of the threat that is lurking in the Welsh mountains. And as another horrendous storm breaks across the hills, the two women's lives are about to take a new turn, but this time they will face the danger together.