Iona Khan got to the pedestrian crossing just as the little green man went out. Drat, she said to herself. Deansgate lay before her. One of Manchester's oldest roads, its lanes cut a wide swathe across the city.

Her thoughts went to the police station tucked halfway up the narrow side street on the opposite side of the road. I'm going to be late. Can't stand being late. Agitatedly flicking one forefinger and thumb, she reflected on why she was visiting the station. It was just over a month since she'd learned that her application for a place in Greater Manchester Police's Counter Terrorism Unit had been successful. Quite a result for someone who'd only joined the force four years ago.

And the timing couldn't have been better: the Labour Party's conference was due to start in two days' time and the Unit was flat out coordinating the security operation.

In terms of profile and importance, this was the Unit's big day. So when Iona was tasked with looking into a report of a foreign student using a false name, her initial reaction was one of disappointment. The assignment meant being marginalized from the Unit's number one priority. No place for her in the daily briefings, no part to play in making sure the conference went smoothly. A simple case of false identity. She'd made sure she didn't appear crestfallen as her boss had handed her the scant details. But, she'd been thinking all the while, couldn't something so inconsequential have waited until after the conference was over?

A car's engine being revved returned her to the present. In front of her, an elderly woman carrying a shopping bag was halfway across the road walking towards her, her head bowed as she took small, determined steps. Not for the first time, Iona thought the traffic lights simply didn't allow long enough for people to get across. The Porsche Cayenne's engine revved again, the vehicle's lines giving it a bullish appearance. Iona glanced at it. Come on, she said to herself. There's no need for that. The woman soldiered on, clearly perturbed by the fact that the safety of the kerb was still a dozen feet away. As cars in the far lanes began moving again, Iona realized the traffic lights must have started flashing orange.

The Porsche also started inching forward, its thick bumper now overhanging the white lines delineating the crossing point. Iona stepped out to give the elderly lady a hand and the vehicle's horn blared, making both of them jump. The driver poked his head out of the side window, a mobile phone pressed to his ear. 'Oi, the lights have fucking changed!' he shouted. 'Get out of the road!'

Iona pointed to the lady. 'I'm helping her!' She turned to the woman. 'Would you like a hand?'

Her eyes cut nervously to the vehicle menacing her. 'Thank you, yes.'

The driver of the Porsche now started trying to edge his vehicle round them. Iona watched in disbelief until its front corner had come to within inches of the lady's spindly legs. Right, that's it. She reached into the jacket of her brand-new trouser suit and produced her warrant card. 'You!' she barked, thrusting it towards the windscreen. 'Take your foot off the pedal. Now.'

His mouth dropped open. Yeah, Iona thought, you're not the first person to be surprised by someone like me having a police badge. The tone of the engine dropped, as did the driver's hand holding the mobile phone.

Iona stood her ground until the woman had made it safely to the pavement. 'OK, missy?' the driver called out amenably. 'OK for me to go?'

Missy? She regarded the man behind the