Stonelea Cat Sanctuary features in several of the existing Home Farm Twins titles, and is run by elderly spinster Lucy Carlton. When Lucy has an accident, she is laid low for several weeks and can't manage all the cats on her own - so the twins move in to help during their school holidays. Every day they are up early at the sanctuary, helping out with abandoned and injured cats and kittens - each with their own special story.

It's time for the twins to say goodbye to Stonelea. Little do they know that one cheeky kitten has stowed away in their car. When the twins arrive at Home Farm, Mac jumps out of the car and disappears on to the fell. Helen and Hannah follow him, higher and higher up the fell. But while Mac has no trouble keeping his balance, the girls face a deadly drop. Can they get themselves, and Mac, back down without falling?