The detective turned on a desk lamp and flicked through the grubby papers, looking for more. Giving up, he rang Hoskins’ mobile, and found him at the Red Lion with a bunch of mates.

‘Are you sober, Carl?’

‘More or less, guv.’ Laughter could be heard in the background. ‘Not called for my take on that last Spurs goal, then?’

‘This travel documentation for Lal is incomplete,’

‘Blimey, hold on. I’m going out into the car park where I can hear you.’

When the background noise had gone, Gillard repeated his statement. ‘This is only the last leg, from Dubai to Heathrow.’

‘That’s all that was forwarded from Epsom. I think we got the complete outbound,’ Hoskins said. ‘Can I deal with it in the morning, sir?’

‘No, Carl, because I have to deal with it now. Okay, get back to the footie, I’ll do it.’

Gillard hung up, returned to his own office, looked up then rang the duty security officer at Air India in London. He got passed from pillar to post, having to verify his security credentials three times at a call centre somewhere in the subcontinent, before he received a promise of a call back with the information he required. While waiting, he spent forty minutes online checking which UK airports received flights from Dubai. There were a lot, and he was only halfway through cataloguing them when, at 12.27 a.m., he got the India callback. It confirmed his suspicions.

Zayan Lal had only boarded the Air India flight back to Heathrow from Dubai. Gillard checked Surrey CID’s security contact details, to find they did not have one for immigration in Dubai. It was 2.45 a.m. when the duty officer at the Met police called him back with the information he wanted.

Only then did Gillard check his own phone to find that his long-suffering wife, Sam, had texted him twice in the last two hours to ask if he was coming home or not. It was now too late to ring her back without waking her.

He was dizzy with tiredness by the time he finally got the information he wanted. Lal had returned to Britain not once but twice in the last month. He had taken the Mumbai to Heathrow flight on the Friday before Mrs Roy’s murder, but left the flight at Dubai. He had then caught an Emirates flight from Dubai to Gatwick, arriving on Saturday. On Sunday night, the day of her death, he had departed again from Gatwick to Dubai, hung around for a day or two, then returned to Heathrow on an Air India flight arriving on Wednesday.

The upshot of these complicated shenanigans was that Lal could provide partial documents which appeared to prove he was out of the country on the day Mrs Roy was murdered. But he had doubled back, and was actually in the UK from Saturday morning until Sunday evening. He would have had ample time to kill her and cover his tracks.

Finally Gillard had some circumstantial evidence for Lal. Now all he had to do was arrest him.