‘Good God, no. We hadn’t planned to start printing before the autumn.’ Ireland, who had seemed about to disobey his sister and help himself to a macaroon from a silver dish, suddenly lost his appetite. ‘This is serious?’

‘Wait till you hear. I was waiting for my wife to finish dressing.’ He grinned. ‘You should make it a rule to read your own books, you know. That’s what I was doing, reading one of those books you sent me and that’s where I found it. You won’t be able to publish Poison at Paraleash.’ The smile went and he looked almost fierce. ‘I’ve no hesitation in saying Kenneth Gandolph is a forger and a cheat and you’d be advised to have nothing to do with him in future.’

Ireland’s eyes narrowed. ‘Better know it now than later. What did he do and how do you know?’

From his jacket pocket Wexford took the copy he had made of the diary entries. ‘I can’t prove that the last entry, the one for March 6th that says, F left cigar case in the dining room, went back after seeing me home, I can’t prove that’s forged, I only think it is. What I know for certain is a forgery is the entry for February 29th.’

‘Isn’t that the one about strychnine?’

‘F destroyed twenty rats with strychnine from his dispensary. What a relief!’

‘How do you know it’s forged?’

‘Because the day itself didn’t occur,’ said Wexford. ‘In 1900 there was no February 29th, it wasn’t a Leap Year.’

‘Oh, yes, it was. We’ve been through all that before.’ Ireland sounded both relieved and impatient. ‘All years divisible by four are Leap Years. All century years are divisible by four and 1900 was a century year. 1897 was the year she began the diary, following 1896 which was a Leap Year. Needless to say, there was no February 29th in 1897, 1898 or 1899 so there must have been one in 1900.’

‘It wasn’t a Leap Year,’ said Wexford. ‘Didn’t I tell you I found this out through that book of yours, the Cosmos Book of Stars and Calendars? There’s a lot of useful information in there, and one of the bits of information is about how Pope Gregory composed a new civil calendar to correct the errors of the Julian Calendar. One of his rulings was that every fourth year should be a Leap Year except in certain cases . . .’

Ireland interrupted him. ‘I don’t believe it!’ he said in the voice of someone who knows he believes every word.

Wexford shrugged. He went on, ‘Century years were not to be Leap Years unless they were divisible not by four but by four hundred. Therefore, 1600 would have been a Leap Year if the Gregorian Calendar had by then been adopted, and 2000 will be a Leap Year, but 1800 was not and 1900 was not. So in 1900 there was no February 29th and Ada Hurst left the space on that page blank for the very good reason that the day following February 28th was March 1st. Unluckily for him, Gandolph, like you and me and most people, knew nothing of this as otherwise he would surely have inserted his strychnine entry into the blank space of March 2nd and his forgery might never have been discovered.’