For now, any mistakes could be rectified. Even if an exercise went badly wrong and Danny and Elena ended up being pulled by the police, it could be sorted by Deveraux. Her MI5 clearance was so high that even chief constables would jump at her command.

But it wouldn't be like that with Black Star.

Oxford city centre was less busy than Danny had hoped. It meant the W H Smith store would not be jam-packed with shoppers, and that would make the brush-contact test even more difficult.

The test sounded simple, but it had done on the previous occasion too. As before, they were to carry out a brush contact in which Danny received a small plastic tub – the type usually containing 35mm camera film – from Elena without the operation being spotted by the third party.

The last time they had tried the drill, Elena had dropped the canister at the very moment she was meant to pass it to Danny. It had bounced onto the floor and another shopper had picked it up and given it back to Elena while Danny walked on. That was it: there were no second attempts once the move had failed.

This time they had to get it right.

Elena was the sponsor of the operation; meaning she had planned the contact. It was likely that if this happened for real, she would be the one making decisions on the ground, passing on information she had gathered about the 'target'. Danny would never be in overt contact with her. As far as Black Star was concerned, Elena was on her own.

She had left her brush-contact orders at a DLB she had chosen earlier: the gap behind a washbasin in Starbucks. Danny had collected the orders and was walking through the city centre shopping precinct. He kept his head down, but not too much – just enough to avoid the direct line of the CCTV cameras. The whole idea was to look natural and avoid arousing suspicion. He was feeling nervous: training was going far from perfectly, and his grandfather was never happy with anything less than perfection.