By the time I reached Whispers Under Ground, I had rather settled into the idea that being a Metropolitan Police officer in Peter Grant’s world is a career with a slightly broader job description than advertised. Murder investigations, paperwork and dealing with the general public are one thing. Ancient magic, ghosts and supernatural beings are another. Somehow Peter is expected to manage both, often before breakfast.

And now we can apparently add underground tunnels, strange subterranean communities and a decidedly unpleasant murder to the list.

Whispers Under Ground takes Peter deeper into London’s hidden places, both literally and figuratively. When a young man is found murdered in the tunnels beneath the city, Peter is drawn into another investigation where the ordinary and the supernatural are once again uncomfortably close together. What follows is exactly the sort of increasingly complicated mess that Peter seems to have become remarkably good at finding.

One of the things I continue to appreciate about this series is the attention Aaronovitch gives to the police procedural side of the story. There is a genuine sense that Peter is doing police work rather than simply using his warrant card as an excuse to wander around investigating magical things.

Evidence needs to be gathered. Witnesses need interviewing. Reports need writing. Other officers need involving. Procedures have to be followed, even when the case involves things that most people would consider impossible. It all gives the investigation a pleasingly grounded quality.

And that grounding is becoming increasingly important as the supernatural side of the series expands.

The police procedural realism provides something solid for the fantasy to bounce off. Peter might be investigating magic, but he still has to ask who, what, when, where and why. He can’t simply declare that a supernatural creature did it and expect the Met to put the case down as solved. There has to be evidence, a chain of reasoning and enough of an explanation to convince other people that he isn’t completely losing the plot.

That makes the fantastical elements feel much more convincing.

It also helps that Peter remains a work in progress. He knows more about magic than he did at the beginning of the series, but he is still learning. There are rules he doesn’t understand, creatures he hasn’t encountered before and plenty of situations where the sensible response would probably be to leave well alone. Naturally, Peter being Peter, he tends to investigate instead.

This time around, the underground setting gives the story a particularly atmospheric quality. London has always felt like one of the characters in this series, but Whispers Under Ground takes us beneath the familiar streets and reminds us that there are enormous chunks of the city most of us never see. The tunnels, stations and hidden spaces provide an excellent backdrop for a story about things that are supposed to remain hidden.

I also continue to enjoy the expanding cast. One of the pleasures of moving further into a series is watching the world grow beyond the original handful of characters, and Aaronovitch is doing a good job of making Peter’s circle feel increasingly populated.

And Abigail is a delight.

I really enjoy the little bursts of personality she brings whenever she appears. She has a knack for adding another layer of humour and energy to the story, and she is exactly the sort of supporting character who makes a fictional world feel more alive. I am increasingly invested in seeing what happens to these secondary characters, which is always a good sign in a series.

The humour remains one of the biggest strengths too. Peter’s observations continue to provide plenty of laughs, particularly when he is confronted with something completely ridiculous and reacts with the weary practicality of someone who has apparently accepted that this is simply what his job involves now.

There is also something wonderfully understated about Aaronovitch’s approach to the supernatural. Nobody spends too much time standing around shouting about how impossible everything is. Magic is strange, certainly, but Peter is gradually becoming accustomed to it. The result is a world where the supernatural feels almost mundane, while the mundane business of policing provides the actual structure holding everything together.

And then there is Kobna Holdbrook-Smith.

Once again, his narration is excellent.

He has completely nailed Peter’s voice, giving the character a natural conversational quality that suits both the humour and the investigative side of the story. More importantly, he gives the extended cast enough individuality that everyone feels recognisable without the performance becoming a collection of exaggerated impressions.

His timing is particularly good. Aaronovitch’s humour often relies on understatement, and Holdbrook-Smith knows exactly when to let a line sit rather than pushing it too hard. He also handles the darker and more atmospheric sections with equal confidence, allowing the story to shift tone without ever feeling jarring.

At this point, I genuinely can’t imagine listening to these books without him.

If I have a complaint, it is only that the expanding mythology occasionally leaves me wanting more answers. But that is hardly a serious criticism. The unanswered questions are part of what keeps the series interesting, and I would much rather have a world that feels bigger than the immediate story than one where everything is explained and neatly packed away.

Whispers Under Ground is another thoroughly enjoyable addition to the series. It takes Peter further into the hidden side of London, continues developing the supporting cast and manages to make increasingly outrageous supernatural events feel surprisingly believable.

The trick remains the same, and it is a very good one. Aaronovitch surrounds the magic with ordinary police work, bureaucracy, evidence and procedure. The more realistic the investigation feels, the more convincing the fantastical elements become.

Add in Peter’s dry humour, an increasingly enjoyable cast, plenty of weirdness and Kobna Holdbrook-Smith’s superb narration, and you have another cracking entry in the series.

At this rate, I suspect Peter is going to need a bigger notebook.

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