‘No other details – like this woman’s address?’

Slater shook his head. ‘Looks like the ball’s in your court, Mr Prince.’

Fortunately Bartholomew was in the office and they began to make plans. Bartholomew would have a team watch the Midland Bank in Threadneedle Street and arrest the woman once she had withdrawn the cash. He’d make sure every exit was covered. He’d even have people behind the counter.

Prince went to the records department in the basement and asked them to check on a Miss Myrtle Carter. A friendly woman with a Welsh accent told him she’d recently reorganised all the watch lists and they now had a centralised record of all the names on those lists. ‘When I took over, there were more than two dozen separate lists, would you believe: lists of people wanted by the police, deserters from the armed forces, people who’d applied to travel abroad now that it’s possible, political extremists… It was utter chaos, my love. Those individual watch lists still exist, but what I’ve done is create an alphabetical list of names of everyone on them. It’s been invaluable. We’ve even spotted people on as many as three different watch lists! It’s made the work of this section so much more efficient, but naturally my senior officer has taken all the credit. Now then, what did you say her name is?’

It took her less than a minute to find Myrtle Carter on her centralised list, along with a reference to where to find her in the original watch list.

‘Here we are: Carter, Myrtle – she’s applied for a permit to travel by ferry to France, accompanied by a Mr Harold Hamilton, both of them with an address in Bayswater. Looks like my system works a treat, eh, my love? Try and make sure I get some credit.’

But when Prince returned to his desk, there was the message to call Tom Gilbey and then the summons to St James’s.

Pop in for a chat would you Richard – later this morning perhaps?

Prince was persuaded to return to MI5 that afternoon while arrangements were made to fly him out the following day. In the time he’d been away at MI6, Bartholomew had made progress, and now they were in Hugh Harper’s office and Sir Roland Pearson had joined them. Bartholomew spoke first.

‘The address in Bayswater is a large house with a dozen or so bedsits. No sign of either a Myrtle Carter or a Harold Hamilton: they’ve never been there as far as we can tell, nor do they receive mail there. It’s what we call a postbox, which means it was probably used solely for the purpose of providing an address for registering their national identity cards. Once these came through, their contact in the house would have moved on. It’s not used as a safe house or as a place to receive messages. We won’t find where she or this Hamilton chap are through this address, and there’s no record of her anywhere else.’