‘But you do not. You have been attempting to open that box. Fruitlessly, I might add.’

He picked up a large envelope which had arrived for him, opened it and gave a shout of delight. ‘Ah! Files on the Cavendish Laboratory. I have an inside track there, Watson. I have learned a bit more of Cosimo Fortuny’s work. Fascinating!’ He eagerly removed a stack of files, tossing the envelope onto the floor.

Mrs Hudson brought more coffee. She skulked out with a glance at the littered floor, clearly irritated at Holmes’s continual additions to the disarray.

‘Holmes, I’m going to try that second locksmith you named – Boobbyer?’

‘Do go, dear fellow, I must read these files. You’ll be back in an hour, I warrant. Then we are off to visit Santo Colangelo. I have gone to the address Madame Borelli gave for her former flame while you lingered abed this morning. It seems he has moved on to cheaper lodgings. I sent him a note, and he has agreed to see us. Go, Watson, have your consultation with Boobbyer!’

My visit to the second locksmith was a disappointment. Mr Boobbyer, a kindly old man with an eyepatch and a pendulous lower lip, attempted for fifteen minutes to assail my mysterious box. He then handed it back, unopened.

‘Trick lock,’ he said. ‘Specialty item. No one can open this. You’ll need the key, and instructions.’

‘What do you mean a trick lock?’ I demanded.

‘I mean it’s tricked. Picking won’t work. It will either take more than one key or something like a key partially inserted, turned, then inserted further and turned another way two times, followed by pressure on this little lever – some odd combination like that. Unless you know how to open this lock, you won’t be able to.’

‘I thought all locks were assailable in some fashion,’ I said.

‘No, they are not. Would you like me to try drilling it open?’

I hesitated. Not knowing the contents, or their placement in the box, I was leery to progress to this. ‘Let me consider it,’ I said, and pocketed the box.

I arrived back at Baker Street in a surly mood, aggravated by Holmes’s irritation at having been made to wait. We then set out at once for Colangelo’s new address.

The rain had done nothing to dispel the tropical heat which suffocated London. As we rattled towards the Strand past limp plane trees and drooping pedestrians, Holmes exuded a jittery energy I had seen often enough when he had not enough to occupy that great, churning mind.

Borelli’s fate was of marginal interest to him, of that I was sure. Holmes was convinced the fellow could look after himself and was perhaps even guilty of rigging his own accident. Nevertheless, he had promised Ilaria Borelli to investigate her former lover, magician Santo Colangelo, to determine conclusively his involvement with last night’s near fiasco.