I do not know if this is the case, but this book reads as if the author is more interested in computers than in Doctor Who. Inevitably, the computer stuff now sounds dated, and I have to say I found it rather tedious. The story becomes a sort of road movie for computer hackers, which makes it sound more exciting than it actually is. The Doctor could almost be any action hero and Peri is not well drawn as a character. The alien element has the potential to be interesting but is largely just a vehicle for more shenanigans with phones and computers. If this were filmed it would be very far removed from Doctor Who, and it largely misses the essence of the show and characters. Got bored in parts, especially near the end. The author clearly wanted to write a computer based story and it feels like using Doctor Who was a way to get that read more than anything else. Not recommended.
A nice story that finds something new to do with the show. A grounded tale of hackers, told through the eyes of a fun, interesting narrator, made more eerie by the true menace being all too human and all too understandable.