THE GREAT walled city of Silasta in Sam Hawke's fabulous debut novel City of Lies (Bantam, £12.99) views itself as a beacon of civilisation in a brutal world, a place of peace and learning.

[[{"fid":"9004","view_mode":"inlineright","fields":{"format":"inlineright","field_file_image_alt_text[und][0][value]":false,"field_file_image_title_text[und][0][value]":false},"link_text":null,"type":"media","field_deltas":{"1":{"format":"inlineright","field_file_image_alt_text[und][0][value]":false,"field_file_image_title_text[und][0][value]":false}},"attributes":{"class":"media-element file-inlineright","data-delta":"1"}}]]Its citizens take it for granted that their high opinion of themselves is universally shared, until Silasta falls under siege from an unknown army, for an unknown reason.

Silasta's armed forces are away in another part of the continent and, in any case, the skills of soldiering are not much valued in this aristocrat-run society. Communications between the city and the outside world have been efficiently sabotaged, suggesting that, whoever the besiegers are, they have the support of a fifth column.

As it becomes clear that the enemy at the gates has no interest in negotiation, a population hopelessly unprepared for war must somehow turn itself into a resistance movement capable of holding out until help can be summoned.

We mainly follow the efforts of a sister and brother who play the part of hangers-on in the court of the heir to the Chancellery but whose family has secretly protected that of the Chancellor for generations. In a state where political disputes are traditionally solved by means of poison, this is far from a sinecure.

This self-contained first part of a series introduces an exciting new writer. She is very aware that, even in a quasi-medieval fantasy world, you can't have an upper class unless there's a lower class and you can't have classes without class war. More than that, one of the engines of her plot is the idea that "I didn't know" is never an adequate defence.

I look forward to more of her rich, tense, atmospheric writing.

It has to be said that Ben Aaronovitch's Rivers of London sequence, of which the latest is Lies Sleeping (Gollancz, £16.99), is beginning to develop a spot of arterial plaque in the form of backstory — the longer the series goes on, the harder it is to recommend that "new readers start here."

[[{"fid":"9005","view_mode":"inlineright","fields":{"format":"inlineright","field_file_image_alt_text[und][0][value]":false,"field_file_image_title_text[und][0][value]":false},"link_text":null,"type":"media","field_deltas":{"2":{"format":"inlineright","field_file_image_alt_text[und][0][value]":false,"field_file_image_title_text[und][0][value]":false}},"attributes":{"class":"media-element file-inlineright","data-delta":"2"}}]]As a Doctor Who writer, Aaronovitch will be familiar with this problem. It's one of the disadvantages of the current fashion for story arcs in place of discrete episodes.

A more serious consequence of arcing, and one which has bedevilled 21st century Doctor Who, is what might be called "grandeur inflation," in which a small grain of portentousness accretes into an indigestible pearl of self-importance, forcing each story to be more pompously significant than the last, squeezing out smaller, more intimate tales.

I'm glad to say there's no sign at all of that in the adventures of DC Peter Grant, apprentice wizard with the Metropolitan Police. On the contrary, what makes these books stand out in a crowded subgenre is that Grant's life remains that of a workaday copper in a country laid low by austerity.

In this instalment, he and his colleagues are struggling to prevent the awakening of an ancient power intended to bring London to its knees. Therefore, defeating evil wizards and placating river gods is inevitably an important part of his work, but no more so than getting his risk assessment forms filled in, ensuring that facilities for holding supernatural prisoners are PACE-compliant, and bagging any decent overtime that's on offer.

Aaronovitch is writing proper police procedural novels, which are at the same time proper novels about the myths and legends of London. His characters are ones you'll want to come back to, his plots are convincingly contemporary and his humour is well-judged.

Altogether, this is one of the most satisfying series currently available.