Alex Scarrow 
TimeRiders (Book 1) 

Liam O »Connor should have died at sea in 1912.
Maddy Carter should have died on a plane in 2010.
Sal Vikram should have died in a fire in 2029.
Yet moments before death, someone mysteriously appeared and said,  »Take my hand . . . »
But Liam, Maddy and Sal aren »t rescued. They are recruited by an agency that no one knows exists, with only one purpose – to fix broken history. Because time travel is here, and there are those who would go back in time and change the past.
That »s why the Time Riders exist: to protect us. To stop time travel from destroying the world . . .