While homages to Agatha Christie abound, it's actually a futuristic action thriller we have on our hands here.

You can invoke reverse gears on any mental meanderings as to what that title might mean; it evokes a cosy update of Agatha Christie; in the vein of The Robots of Death or The Murder Game, as suspects diminish in number in inverse proportion to clues and red herrings and actually the butler did it...

No. While homages to Christie both superficial (chapter titles) and deep (a mystery, a dark and isolated location, dramatis personae individually bumped off) abound, it's actually a futuristic action thriller we have in our hands here; the presence of the eponymous aliens being more significant than the precise number we're dealing with.

The first Doctor's presence seems indicative of a mismatch of concepts - try as I might, I can't mentally place William Hartnell and Sigourney Weaver in the same frame - but Ben and Polly, are always welcome returning visitors. Outside of this trio, there is a small cast of characters, cheerfully introduced to us via what is effectively a Smash Hits cut out-'n'-keep fact file of their personalities - the most effective shorthand I've seen in a Doctor Who novel in some time. This hungry bunch is on a mission to combat warmongering adversaries, the Schirr... and although dark and moody spaceships and their requisite shadows, corners and clanking footsteps are rather more the stuff of visual or even aural entertainment, I'm a sucker for the environment...

There is, though, a further stylistic conceit which sends the denouement into a tailspin; we encounter a multi-stranded journey toward confrontation, which is not to be read linearly. A fair idea, but its sudden appearance here a few chapters from the end left me unsure as to which path to take, or indeed whether to cry "Sod the instructions!" and read the words in the order they were presented to me. It might have been more suited to a much earlier part of the explorations, or even an entire, intriguingly-structured novel in the vein of Eye of Heaven. As it was, not unexpectedly when faced with a labyrinth of possibilities... I got lost.