In the end, this is what his home revealed:

The notes from his diary

Six new and expensive paintings on the wall

The business card of a very high-class art dealer

Another card, from a house whose reputation I knew, a mile away

An ingeniously concealed wall-safe with a lock that took me nearly two full passes of the constable to circumvent.

Inside the safe I found a velvet pouch with a palmful of large-carat diamonds, three stacks of high-denomination currency (British, French, and American), a number of gold coins, a file with memos and letters signed with Mycroft’s distinctive M, and a bank book dating back to 1920.

The file included a trio of carbon pages requesting information on Thomas Brothers and Marcus Gunderson. They were pinned to a copy of the Brothers photograph that Mycroft’s Shanghai man had brought, and another of a glaring Marcus Gunderson.

The bank book was the most revealing. For years, the entries down the IN column varied little, and seemed to comprise his regular salary and periodic income from stocks and an inheritance fund. Until the past March, at which time round sums began to drop in at untidy intervals: twenty guineas here, thirty-five there. In the middle of June was one for a hundred guineas.

I had to smile sadly at the idiocy of criminals: caution and carelessness; locked doors beside vulnerable windows; scrupulously kept books recording illicit income.

Then I looked at the last page, and the smile died:

Friday 29 August: 500 guineas received.

The day after Mycroft disappeared.

Five hundred pieces of silver.

I left everything where I had found it: I had the name of the bank, the dates of the deposits-along with information on his art dealer, his newsagent, his housekeeper, his solicitor, and his mother. It would be of interest to examine the mother’s account, although I did not imagine it would show those round sums in its OUT column.

It was nearly time for the constable to pass, so I stood at the curtains with my torch off, waiting for the deliberate footsteps.

Sosa was in his fifties, an age when some men looked up and saw not what they had, but what they lacked. This was particularly true when a man was under pressure-and between December and March, when Mycroft came back to work after his heart attack, the pressure on his assistant would have been considerable.

The major question in my mind was, when did Mycroft discover Sosa’s hidden income, his secret life, his-call it what it had to be-treason?

It was hard to picture the grey man working day in, day out under Mycroft’s very nose without giving himself away. But until this past month, I had not seen Mycroft since the early weeks after his attack, at which time he had been both ill and distracted. I could not deny the possibility, however remote, that he could have overlooked his secretary’s treason until very recently.

Ten days ago Mycroft had talked to Sophy Melas about loyalty. Where does faith part from loyalty?

He knew then.

Did that knowledge get him killed?

Or had he known for some time, and done nothing, either because he was testing the limits of his secretary’s betrayal, or-and this I could envision-because he was using Sosa to lay a trap for the man or men behind him? I could well imagine Mycroft keeping an enemy close for half a year in order to tease out the extent of a conspiracy. He might even have embraced the challenge of proving that his illness had not lessened his abilities: to work every day cheek-to-jowl with an enemy, blithely feeding him information, never letting slip once.

A Russian doll of a mind.

Had that hubris got him killed?

And was there any way in which Brothers entered this mix? There was no copy of the man’s bible, Testimony, on Sosa’s shelves, and I had not seen him in the Church of the Light services that I had attended. Was it possible that whoever was backing Thomas Brothers was also responsible for suborning Mycroft’s secretary? As I’d told Billy, simultaneous timing did not prove consequence, but coincidence still bothered me.

The constable approached, then passed. I let myself out of the Sosa apartment, leaving the ivory frog where it lay, and managed to lock the window before I left.

Several late-plying taxis passed me on the walk to Baker Street, but sure knowledge of the conversation a taxi-ride would entail-either the driver would think a young woman out on her own at this time of night was no better than she should be, or he would wish to rescue her and watch over her every move until she disappeared through the doors of a house-forced me to walk, reminding myself at every step that I should dress as a man for every night-time expedition. However, the bolt-hole was not far out of the way from my next destination: I could effect a change there.

Under-slept, over-walked, and distracted is no way to approach a secret hide-out, and I was lucky the only person lying in wait was a blond imp, who dropped light-footed from a first-storey archway and scared me to death. I cursed him and came near to kicking him, and in an ill temper stalked towards the entranceway.

“Why are you out here?” I snapped. “Did you forget how to get in?”

“The city at night is a restful place,” he said, which was no answer and was patently untrue-my own night in this city had hardly been restful. “I am happy to see that you were not arrested.”

I looked up from the locking device, my eyes narrowed with suspicion. “How do you know what I’ve been doing tonight?”

“I don’t. What have you been doing?”

“How-ah.” I turned back to the lock: He was not talking about my house-breaking. “I neglected to tell you what was in that letter in Mycroft’s flat. It would appear that the police have decided my husband and I are no longer of official interest.” I explained what the note had said, and who had sent it.

“So you can come out into the open? You and your husband?”

“Probably not. For one thing, it’s possible that Lestrade might be thinking to lay a trap, either for us, or to lead him to Damian-my stepson, Yolanda’s husband.”

“Estelle’s father,” Goodman said, adding, “Who is too claustrophobic to go to gaol.”

“Are you?” I asked. “Claustrophobic?”

“Not in the least.”

“Good,” I said, and opened the door to Holmes’ bolt-hole, which was so snug and stuffy, a hibernating squirrel might become uncomfortable.

While Goodman set about exploring the nooks and crannies of the space carved into the interstices of the buildings, I did what I should have done on our earlier visit: Review the supplies and check the ventilation shaft, lest some bird had plugged it with a nest.

All was well: food, drink, electrical light, and air, along with entertainment in the form of books, a chess set, and playing cards. There was even a serviceable bathing facility, cramped but equipped with warm water diverted from the neighbouring building.

I showed Goodman where everything was, then told him, “If anything happens to block the entrance, the alternative exit is down here.” He peered with lack of enthusiasm into the duct, but in an emergency, I felt certain, he would manage. “In the winter time it’s a little tricky, because the building’s furnace is at the bottom, but it should be fine for now.”

“You are leaving again,” he asked, although it was not a question.

“I have to speak with Lestrade. He may not be in charge of the investigation, but he’ll have kept a close eye on its progress. I’m going to write a letter to Holmes before I go. If I’m wrong about Lestrade and he has me arrested, everything Holmes needs to know will be in the letter-if you see him, tell him it’s here. But after that, I recommend you make your way as quickly as you can back to Cumbria. With, may I say, my considerable thanks.”

I put him into the bedroom, warning him to turn on a light when he woke-even he might bash his skull by rising incautiously. When I was alone, I changed my clothing, then sat down to record everything that had happened since Estelle and I had parted from Holmes and Damian, eight days before: the suggestive lack of police interest that night in Orkney; the sniper in Thurso; the crash and rescue; five days in the Lake District cut short by men with guns, and how they might have found us; leaving Javitz and Estelle at the house in Richmond; what Billy had said about the “hard men;” what I had found in Mycroft’s flat (this I worded with great care); the interview with Sophy Melas; and what Sosa’s home had told me.