He studied them with deep stern eyes hidden between furrowed eyebrows andsallow cheeks etched with criss-crossing wrinkles.

‘Mankind was never meant to dabble with time. Never! Butnow that we know how to somebody needs to make sure that nobody actually does so. And, if some fool does go back in time, then it’s someone’s jobto fix the damage caused as quickly as possible.’

There was a faint tremor in his rasping old-man’s voice.

‘Time travel is a terrifying weapon, far more powerful than anything ever beforeconceived,’ he said grimly. ‘Mankind just isn’t ready for that kind ofknowledge. We’re like children casually playing toss and catch with an atombomb.’

Liam cocked his head questioningly. ‘What’s an atom b-?’

‘I’ll explain later,’ replied Foster. ‘Which brings me to you three,and this place,’ he said, gesturing at the darkness beyond the pool of light. ‘Thefact is there are too few of us TimeRiders — groups like us dotted around the world,dotted through time, watching and waiting patiently.’

‘Watching for what?’ asked Maddy.

‘For a shift.’

‘A shift?’

He nodded. ‘It starts as something ever so slight, almost unnoticeable to the eye. Youcatch it then, when it’s just a ripple. You have to because, before you know it, itbecomes a tidal wave; it becomes unstoppable, uncontrollable. And then we’re all trulyscrewed.’

Sal’s eyes had been lost in the darkness, still far away, but she turned to look atFoster. ‘What is a shift?’

‘A shift is the result of time being disturbed.’

Foster pursed his lips in thought for a moment. ‘OK, think of it like this: time is like a still pool, or a bath. Have you ever tried stepping into a bath without creating a ripple? It’s impossible, isn’tit?’