The Magic Helmet (White Early Reader) : A Viking Adventure

When Harry finds a magic helmet in his grandma's garden and puts it on, he's transported back in time! He finds himself on a Viking longboat and learns a lot about how they used to sail, plunder and bury their fallen men. But the best thing he learns is that his missing grandad isn't acutally missing - he travelled back too and now he's the Viking leader! Illustrated by Dean Gray.