It seems like nearly every Doctor Who book is frustrating in some way. This makes sense, considering the conditions they were created under - licensed books that were sold on the strength of the brand rather than the strength of the authors involved. They often involved writers new to the craft of novels; writers who were valued for productivity over quality; and writers who had been involved with the property for years - in a different medium. And this turned out many books that were frustrating in fascinating and valuable ways, books that transcended the problems of the format to create something interesting and fun that could only have been created in this time and place.
Not this book, though.
I mean, the concept is something that could only be created in a context like this - to save the Earth without the Doctor, the supporting characters of different Doctor Who eras have to team up with Earth's worst enemy! But what should be a fun adventure with a bunch of interesting character moments turns into a slog.
The problem here is that this is a book with many deep and complex characters in it that it stubbornly refuses to treat as deep or complex - no, even worse; that it builds an interiority for based on shallow cliches and basic tropes, and then confidently proceeds forward as if this were all the complexity there was in a human soul. The pre-existing Doctor Who characters become broad sketches of themselves, the stock character archetypes that you'd assume if you had no familiarity with the series and someone described them to you in broad detail. (Barbara takes the worst of this; the woman with the hubris to try to overthrow an entire civilization for the greater good, and the wit, spirit and determination to almost pull it off, is attenuated into a plucky, didactic, worrisome schoolteacher.) The new characters are those stock archetypes, thinking loudly about their one-note motivations; they're based firmly in perspectives on the world that are supposed to feel "gritty" and "real", but feel more like the perspective of someone drained of empathy and vitality by the pre-Thatcher era, watching the news and trying to come up with a theory as to why cops, criminals and terrorists acted the way they did. Both groups get the occasional good moment - the primary antagonist, in particular, has a sympathetic moment near the end which almost fleshes her out into a full two dimensions - but moments are all there is.
The one exception to this is the Master, who's allowed to be his gleeful, chaotic, indulgent self; who values drama and style almost as much as taking over the world; who understands people deeply but can't bring himself to truly believe that understanding, because it would mean they aren't sheep, aren't a resource to be exploited, and that he is and always has been the worst thing possible - wrong. He feels, if not three-dimensional, an interesting two-dimensional slice of a three-dimensional character. (He's clearly David A. McIntee's favorite character here - this book heavily references the book he wrote about the Master's backstory, The Dark Path, and also throws in refs to another book of his with the Master as the antagonist, Final Frontier.)
The Master pulls my rating up to two stars, but no higher; he can't save this from being a boring book, one that thinks it's far more exciting and complex than it actually is. Not recommended.