When Tom and Polly marry, blending their single parent families together, their children find it hard to relinquish their old lives. Max realises his birth dad will never come home now, while Abi suddenly finds herself a middle child, expected to share far too much - especially with grubby little Louis. The family start over together, stretching their finances to the limit and renting an eerie, ivy-covered house, big enough for all of them.

But when the children are alone there, strange things start to happen. Worried, Louis summons comfort from outdoors, and a startling guest arrives - is it a cat, or an owl, or something else? Abi reads alone, tumbling deep into books. Max loses his best friend and falls in love.

Meanwhile, Louis’ secret visitor is becoming much too real. And when Max and Abi too start to see the great spotted cat-thing that arrives in the night, it becomes a problem the three of them must find a way to solve - together. But where has the creature come from, and how will he get back?