The year is 1935. Clive Staples Lewis (known to his friends as 'Jack') and his brother Warren ('Warnie') are visiting their friend young Tom Morris at Nesfield Cathedral School - where Jack is to be guest speaker at the school's speech night. They become eyewitnesses to a murder-an impossible murder.

'Dear Jack, I think I'm about to be arrested and charged with murder.' Tom Morris, busy cataloguing the library of Plumwood Hall, is in a fix. Three days before, a member of the family had keeled over at afternoon tea after eating a slice of fruit cake laced with poison. And Tom has been fingered by the weasel-like Inspector Hyde as chief suspect. The young scholar turns to the only person who can help: his old Oxford tutor, C. S. ('Jack') Lewis. As they investigate, mystery piles on mystery. Why did the victim's husband disappear twelve months before? Why is a strange tattooed foreigner...

It's a Thursday evening in 1936. Clive Staples Lewis (known to all his friends as "Jack") is hosting a gathering of that well-known literary group, The Inklings. Among the regulars are his brother Warnie, J. R. R. Tolkien, Neville Coghill, Hugo Dyson and Adam Fox. Two visitors are also attending - Jack's old pupil Tom Morris and an undergraduate named Auberon Willesden. The following morning Willesden is found murdered in his room in Magdalen, though both the door and the windows were locked from the inside. And not only has he been murdered: he has been beheaded - and the head is missing! ...