Johnny and the Bomb by Terry Pratchett

Terry Pratchett is always side-splittingly funny. In Johnny and the Bomb, my first encounter with Johnny Maxwell, there is a delicious undertone of irony. The author's wry portrayals of the young heroes and heroine can make you want to laugh and cry. "Don't tell me we're going to have an adventure with me and four token boys," Kirsty exclaims in disgust at the beginning of the story. These are tragi-comic figures in some ways - they see the world with post-modern eyes and I couldn't help feeling a pang of nostalgia for simpler times when adventures would be welcomed unquestioningly with open arms:)
Travelling in time has become a well-worn narrative. There are certain conventions in time travel stories now: If you go back and change something in the past, the present you return to will be either unrecognisable or changed in subtle ways. You require a machine to do time travel in. Johnny and the Bomb shines because of its play with these conventions. Gunk inside a garbage bag in a shopping trolley can transport you in time. Also, if you can run in space, you can also run through time. Who knew? It doesn't overturn all conventions, it plays with some, it adheres to others. 
It is imbued with Pratchett's deep respect for human life. A death in a Pratchett novel is not an easy occurrence. His young protagonists are tested to the very limits of their ingenuity in their quest in this book to save twenty lives in a WWII bombing.
This book is a delight because of Pratchett's style of storytelling, always ethical, always critical and always funny.