And so they began, Cranston occasionally pausing for refreshment as he recited in an almost sing-song voice what they knew about Springall’s death, and then Brampton’s, Vechey’s and Allingham’s. Athelstan would correct him and make Cranston repeat the list of facts time and again until the coroner, not famous for his patience, shouted: ‘Hell’s teeth! What are you doing, Brother? We are wasting time! All we are doing is repeating what we already know.’

‘Be patient, Sir John,’ Athelstan replied, ‘Remember, we are looking for a pattern. In logic when you have a problem, the very words of the puzzle contain the answer. There must be a pattern in each of the murders.’ He saw Sir John set his mouth and glare from beneath bushy grey eyebrows. ‘Look, there is one murder we know very little about - Vechey’s. But three, Allingham’s, Brampton’s and Springall’s, we do. There must be common factors, things which link all three. We have already established one: poison. I also suspect Vechey and Brampton were drugged. They would not have allowed people to pluck them up, take them prisoner, tie a noose around their necks and kill them. So we have some matching strands. Let us see if there are more.’

Once again Sir John grudgingly recited the facts they knew. Outside the day drew to a close. Athelstan, now listening with half an ear to Sir John’s recitation, looked out of the window and wondered what had happened to Benedicta and Lady Maude. Should they return to escort the ladies? He broke Sir John’s concentration by asking but the coroner just glowered.

‘The Ladies Benedicta and Maude are well able to look after themselves,’ he said. ‘You started this, Brother, so we’ll see it through to the bitter end. Moreover,’ he smiled, ‘I asked the young gallant who was sitting by Benedicta to take care of both ladies. I am sure he will.’

Athelstan ground his teeth and glared at the coroner but Sir John smiled sweetly back as if innocent of any devious stratagem. Athelstan again made him repeat all they knew, though this time excluding Sir Thomas Springall’s murder. Then he walked over to the window and stared down at the chess board. Absentmindedly he began to count the squares, and his heart quickened.

‘There is a pattern, Sir John,’ he said softly. ‘Yes!’ He turned, his lean face bright with excitement. ‘There is a pattern!’

‘You know who the murderer is, don’t you? Come on, you bloody friar!’ Cranston roared. ‘Tell me! I haven’t sat here on this bed like a boy in a schoolroom reciting lists of facts for nothing!’