Johnny And The Bomb - Terry Pratchett
Johnny Maxwell and his friends have to do something when they find Mrs Tachyon, the local bag lady, semi-conscious in an alley . . . as long as it's not the kiss of life.
But there's more to Mrs Tachyon than a squeaky trolley and a bunch of dubious black bags. Somehow she holds the key to different times, different eras – including the Blackbury Blitz in 1941. Suddenly nowisn't the safe place Johnny once thought it was as he finds himself caught up more and more with then . . .
The third book in the Johnny Maxwell trilogy.