Spoiler-free synopsis
Maggie Barnes lives alone in London, with few close relationships and little confidence in herself. The prospect of helping MI5 gives her a chance to feel useful in a way her ordinary work does not. What appears to be an opportunity to do something important leads her into a story of danger, manipulation and uncertain trust.
This standalone is best approached knowing relatively little. It offers the attractions of an intelligence thriller while centring someone far outside the professional ensemble of Slough House. Maggie's loneliness matters as much as the apparent mission: an invitation to significance can be powerful when someone already feels easy to overlook.
Reading order
There is no preceding Maggie Barnes novel to read, and no numbered place to find in the Slough House sequence. Choose This Is What Happened when you want a self-contained story that uses Herron's interest in secrecy on a more intimate scale.
If you came to Herron through Slow Horses, allow a different rhythm and cast. The central appeal here is the uncertainty around one woman's position. Starting without a list of expected intelligence-world connections gives the opening room to establish its own terms, and prevents familiarity with Lamb's office from deciding what you think is happening.
Being noticed
Maggie's isolation is an effective basis for suspense because it makes attention itself significant. Someone offering her a special role can seem to recognise qualities the rest of her life ignores. The same promise also creates vulnerability: wanting to matter can make it difficult to challenge the person who says that you do.
That is a more unsettling starting point than a simple contrast between innocence and professional skill. An inexperienced person can still make decisions, but may not have reliable ways to judge the information offered to her. The reader's task is to pay attention to how the opportunity is described, who explains it and what alternatives remain visible.
Plot: the mission changes shape
Reveal the opening operation and its consequences
Harvey Wells recruits Maggie to install spyware on her employer's computer network using a flash drive. She enters the London office building late at night to carry out the task. The operation goes wrong, and the apparent spy story becomes a much more claustrophobic examination of Harvey's hold over her.
Maggie's relationship with the man who recruited her becomes central. Publishers Weekly describes Harvey as manipulative and the novel as a disturbing portrait of contemporary England. The changing shape of the story makes trust, resentment and control more important than the glamour of the job Maggie thought she was accepting.
How to read the suspense
Notice the difference between what Maggie experiences and what another person tells her that experience means. In a story about manipulation, explanations can become part of the pressure exerted on someone. A confident account may be persuasive without being a reliable guide to what choices are available.
Reading slowly enough to register those explanations is more useful than racing only towards a twist. A reversal can be exciting, but the premise also invites attention to the smaller acts that make dependency possible: reassurance, withheld information and the suggestion that only one person understands what is going on.
The title promises an account of events, and its plainness makes a good question to carry through the novel. Whose account are you receiving? What would another participant describe differently? Keeping those questions open lets the psychological suspense work without reducing Maggie to a mechanism for surprising the reader.
Television and film
This is a separate psychological thriller rather than a Slough House instalment. The connection for viewers of Slow Horses is Herron's writing, not an expectation that the familiar television cast will appear. Its small central cast offers a different way into his interest in power over people who are easy to underestimate.
Editions and audiobook
The John Murray catalogue includes paperback, electronic and downloadable audio versions. Imogen Church narrates the publisher's audiobook, released on 5 July 2018. That credit applies to the listed recording. Readers choosing another territory's audio edition should use its own narrator information rather than assume every recording has the same performer.