There’s a modern trend for historians to try their hand at fiction. As far as I can tell, it started with Alison Weir’s Tudor novels; more recently, Lucy Worseley and even Neil Oliver have jumped on the bandwagon. Now it’s the turn of Ian Mortimer, a brilliant medieval historian and the author of the various Time Traveller’s Guides to British history. You can understand the appeal. After all, historians have immersed themselves in the modes and manners of their specialist periods and should be perfect guides to fictional recreations of those worlds. But, but, but. Knowledge alone isn’t enough to make a good historical novel. Mortimer’s speculative time-slip moral fable is packed with instructive observations about daily life in the past, but does it work as a story?