July 1940 – as Tarn struggles to come to terms with the loss of her beloved brother in the chaos of the British retreat at Dunkirk, she and her friends scour the hills around their Lake District home, watching for any signs of the long-dreaded Nazi invasion.

But as the war drags on, with little good news from the front, the locals become aware of someone carrying out anonymous acts of kindness, such as saving a flock of sheep from a snowdrift and getting help for an injured farmer who might otherwise have died.

With no one claiming credit, they come to think of this unidentified stranger as a kind of guardian angel, but when his identity is finally revealed, can Tarn come to terms with the truth...?