It is impossible to read The Long Cosmos without a pang of melancholy. Completed 18 months before his death in 2014, it is not the last book Sir Terry Pratchett ever wrote – that honour goes to The Shepherd’s Crown, published last year – but it is the last new Pratchett novel we are ever likely to see.

The Long Cosmos is the final instalment of the five-part Long Earth epic, co-written with sci-fi veteran Stephen Baxter.

The year is 2070AD, and decades have passed since the events of the first volume. “Time just pours away, doesn’t it?” muses the elderly Sister Agnes, a computer-powered nun. “I think my time should come sooner rather than later. It’s right that way.”