By Alex Scarrow

This is the second book in the brilliant TimeRiders series and it carries on the same fantastic vein as the first. Our three protagonists should all have died, Liam in 1912, Maddy in 2010 and Sal in 2029, but they were each greeted by a mysterious old man named Foster at the instant of death and given a second chance at life, working for an agency that no-one knows exists and whose purpose is to prevent history being unravelled by those who meddle with time travel.

Liam, Maddy and Sal receive a partial communication from the future detailing a contamination event. Time has been altered and it appears to be because of the assassination of Edward Chan. They agree that Liam and Bob must use a portal to go back to the point of Chan's assassination to assess the situation but Maddy unfortunately opens a time window by mistake, leaving Liam and a school party of teenagers stranded in time sixty-five million years ago. Now, with a previously undiscovered predatory dinosaur chasing them Liam has to stay alive and figure out a way to make contact with Maddy and Sal without endangering history and putting the world in danger of a whole new reality.

Alex Scarrow has signed a nine book deal with Puffin and after reading this terrific series of young adult novels it's easy to see why. It would be easy to say it's the page-turning action, fast-paced thrills and terrific characters and all of that would be true, but Scarrow has chosen to pose some very difficult questions in these books and it's the way they get you to think that make them stand out. Of course the quandary of the time travel paradox is nothing new, every sci-fi writer and his dog has turned their hand to it at some stage , but for a whole new generation of readers these books will present some difficult puzzles in probably the most entertaining package imaginable.

For starters the team are all from different times and different eras which naturally has an impact on their outlook. Also. they live in a time bubble in New York which loops the forty-eight hours during which the World Trade Centre is attacked and Sal - removed from a building just before it collapsed - is the observer, is tasked with just wandering around the city every day looking for the subtle but telltale changes that indicate someone may have tampered with time. Liam - removed from the sinking Titanic - is the fast-thinking, practical field agent who moves around in time preventing damage and Maddy - removed from a plane crash - is the strategist and soon, despite her reluctance, becomes team leader, making sure the machinery that makes their work possible is running, but also hiding from them the terrible effects what they do have on one member of the team. There is also Bob, or Becks as it becomes, the AI chip that resides in a newly grown body to accompany Liam on his travels and who is developing 'human' traits, not least of which is that she has taken a liking to Liam.

Like I said at the beginning, these are great action adventure stories that really do keep you gripped from front page to back. There is genuine danger and you never really know for certain who will live and who will die - and folk do die - and throughout the story you get tantalising glimpses of the mysterious agency that recruited them and clues that might or might not reveal more about their circumstances but never really giving the game away.

Imaginative, compelling and ultimately huge fun I'd get cracking on these books as soon as possible as this series looks set to just get better and better.

Day Of The Predator is published by Puffin and is available from Play.com, Blackwell and all good book stores.

Alex Scarrow shares a website with his brother, Simon.