In this book, the climax of the trilogy, foul deeds and slaughter abound! Peer and Hilde set sail in the Viking ship 'Water Snake', heading for the shores of Vinland, 'the land beyond the sunset'. Companions on the voyage include Gunnar One-Hand, haunted by ghosts, and his sword-wielding son Harald Silkenhair. Harald has an uncontrollable, raging temper, and a perilous rivalry develops between him and Peer. And that's even before they meet the 'Skraelings' (the Native American people) and the terrifying Jenu - the cannibal giant with the heart of ice...

Did you know that the Vikings reached North America, 500 years before Christopher Columbus? They named it 'Vinland' because they found grapevines there. They also met, and fought with Native American Indians, whom they called 'Skraelings'.

By the way, you'll find the Nis in this book too – I really couldn't leave him behind!

Read reviews of Troll Blood by Amanda Craig and Jill  Murphy.

I was thrilled when my publishers, HarperCollins, asked me for another book – because I knew there was plenty more I wanted to find out about Peer and Hilde and their world. How would their friendship progress? What would Peer do with the ruined old watermill he'd inherited from his uncles? What were the trolls getting up to now? And of course the Nis was bound to reappear!

Also, I wanted to re-use some old northern legends about the seal people – not mermaids, but seals who can transform into humans by casting off their skins. I knew a story about a fisherman who married a seal woman, but was heartbroken when she deserted him and went back to the sea. What would that be like if it really happened?

Troll Fell is a winter book, set among the mountains. Troll Mill turned out to be a summer book, set along the wild Norwegian coastline – with mountains and trolls mixed in as well, of course!

Years ago I had an idea for a book set in Viking times, about a boy and his family. I wrote 20 pages and then got completely stuck! But I liked the characters and the setting, so I kept it. When I moved back to England I found it again, took a look, and saw what was wrong. I'd had Thor and Odin in the story – the old Viking gods – and they didn't work. After all, if all-powerful gods can help the characters out any time, what's left for the hero to do? I decided to get rid of the gods and have trolls and other magical creatures instead.

For a long time I couldn't think of a title for the book, and then one day it came to me. Everything in the book happens on or around a sinister mountain named 'Troll Fell', with a secret kingdom of trolls buried beneath it. I could call the book 'Troll Fell' after the mountain!

My favourite character in the book is probably the Nis – an unpredictable and touchy but good-hearted little house spirit. I didn't 'invent' the Nis – there are lots of Norwegian folktales about such little creatures.