‘You may well be right,’ said William. ‘However, there are one or two matters I still have to clear up. Hamish Buchanan claimed the flask he handed to his father only contained a mild sedative that he had been prescribed by you.’

‘That’s correct. One or two of the family, including Hamish, occasionally suffer from seasickness, so I always have something at hand to help them sleep. In any case, everyone saw Hamish and Fraser drink from the same flask, so there’s no reason to suspect that his death was due to anything other than natural causes.’

Once again, someone had delivered a sentence that wasn’t necessary. William wondered what else the doctor had to hide.

‘Do you have any more of that medicine, doctor?’ William asked. ‘As I don’t suppose I’ll be getting much sleep tonight.’

‘Of course,’ replied Lockhart, who opened his leather bag, took out a half-empty medicine bottle and handed it to William. As he did so, William spotted something else in the bottom of the bag that answered a question he would no longer need to ask.

‘I’ll leave you now, doctor,’ he said. ‘I’m sure Mrs Buchanan will be grateful for your company. But before I go, can you tell me which is Hamish Buchanan’s cabin?’

‘Number three. It’s the first door on the left as you go out.’

‘Thank you, doctor.’ William opened the cabin door, stepped back into the corridor and walked slowly across to number three. He took a deep breath and knocked on the door.

‘Enter,’ said a voice that sounded wide awake.

William walked into the cabin to find Hamish Buchanan seated in a large, comfortable chair, a goblet of brandy in his hand, a half-smoked cigar in the other. There was no sign of his wife.

‘I’m sorry to disturb you at such a late hour,’ said William, ‘but I need to ask you a couple of questions before you go to bed.’

‘No need to waste your time, Chief Inspector,’ said Hamish, not bothering to offer him a seat. ‘I’ve already spoken to my lawyer in New York and he’s advised me not to answer any of your questions until he can be present. He felt sure I wouldn’t have to remind you that this vessel is registered under an American flag. A country in which you have no jurisdiction.’

‘Nevertheless, I do have the commodore’s authority to carry out an investigation into your father’s death,’ responded William. ‘I can’t imagine my questions would worry someone who has nothing to hide.’

‘You won’t get me to rise quite that easily, Chief Inspector, so please leave me to mourn in peace.’ Hamish flicked a piece of ash into an ashtray by his side before adding, ‘My lawyer also advised me that once we enter American territorial waters you will no longer have any authority on board this ship, whatever the commodore says. Therefore, may I suggest you go to bed and try and get a good night’s sleep.’