Following the events of the Key to Time sequence, the Doctor has installed a randomiser in the TARDIS, ensuring that all trips are to unplanned locations and ensuring that the Black Guardian cannot know where to take his revenge. Their first landing takes the Doctor and the newly-regenerated Romana to Skaro, to which the Daleks have returned seeking something...
This story marks the return of the Daleks after an absence of five years, and is the first story in a season with Douglas Adams of 'Hitchhiker's Guide to the Galaxy' fame as script editor. And an odd little thing it is, too.
What I don't like about it is that it fails to take itself seriously enough. (At the risk of sounding like I'm saying "but some of my best friends are...", I don't object to humour in Doctor Who - but it should be a relatively minor element.) Romana's regeneration, essentially because she felt like it, devalues the Doctor's own various regenerations, and the Doctor's taunts of the Daleks plainly reduce their value as an enemy. A bit more thought, and less obsession with humour, could have handled these things much better.
And then there's Davros. After 'Genesis of the Daleks', it became impossible to have a Dalek story without Davros in it. Why? I also have a problem with the old "such-and-such is a genius, therefore they can do anything" theory that surrounds supposedly brilliant scientists. Davros' knowledge is thousands of years out-of-date, there is no reason to assume that he can provide the Daleks with the technological advantage they are seeking.
This book (and the video of the same story!) are certainly not a high point in Doctor Who's history.