The children of Twigswick are taught three things-

1. Never stray past the rune posts at the edge of town
2. Run home as fast as you can when the warning bell chimes
3. Spirits are very real and very dangerous

Nettle Sourbud lives in the shadow of her older sister, Fern; fearless, tough and confident, Fern is everything Nettle is not.

So, when Fern runs off to join the Wildheart Rangers - the protectors of towns from the spirits and ghouls of Dryda Forest - Nettle thinks she's lost her sister forever, as she'll never be brave enough to follow her into the enchanted woods.

Then news reaches Twigswick that Fern has abandoned the Rangers to join the infamous Shadow Stalkers and Nettle knows something isn't right. Fearing her sister is in danger, she ventures into the forest to find the truth . . .

Joining the Rangers, Nettle realises she'll have to face her fears and defeat the Hollow Spirits who haunt the forest if she wants to rescue Fern. But soon Nettle starts to wonder if her sister needs saving at all, or Fern is the one who must be stopped . . .