London police constable Peter Grant investigates two cases in Soho, both apparently involving the supernatural. Police Constable Peter Grant works for the Folly, a semi-secret department of the London police department that deals with the supernatural.
In the first book of the series (Rivers of London/Midnight Riot) discovered magic was real and was recruited by his boss DC Nightingale as an apprentice and only other human employee of the Folly .
At the start of Moon Over Soho Nightingale recovering from injuries sustained in their previous case and Grant is called in to investigate the sudden death of a jazz musician. Although it looks like natural causes the body shows evidence of ‘vestigia', the magical residue left from a magical event or presence.
Grant goes to his father, a well regarded former jazz musician known as Lord Grant for advice. He needs a version of a song which he heard lingering magically as part of the vestigia. They narrow it down to a specific musician who died in a 1941 bombing while playing at a local club during the blitz.
Grant also visits his old cop partner Lesley May, who suffered terrible damage to her face from a magical possession during the events of the first book. She is on medical leave and living with her father, but she is interested in the case and helps Grant by text and email. She asks whether her injuries can be magically cured and he says no, although he wonders about it later.
The coroner informs Grant that there have been an unusually high number of deaths among jazz musicians in London in the past couple of years.
Grant makes friends with the victim's former bandmates during the investigation, and they end up tagging along during part of his evening, impressed when they learn who his father is. He later helps them by having his father join their band, Lord Grant is recovering from an addiction problem and glad to be playing music again.
They check out the jazz club where one victim died, and while there he notices the same lingering vestigial song, this time associated with a trombone. He checks the dressing room but the only person there is a woman who says the trombonist just left. Grant follows after him, but arrives to find an ambulance picking up the trombonists body, who has apparently just collapsed and died.
Meanwhile the police are also investigating a series of gruesome murders of men apparently caused by some a pale woman with dark hair, also in Soho. Detective Sergeant Stephanopoulos, head officer of the Murder Investigation Team calls Grant in as a consultant due to the unusual bite patterns that suggest this woman is more than she seems.
While tracking down clues Grant runs into Simone, the ex-mistress of the first jazz victim. He flirts with her, and they soon start sleeping together at the apartment she shares with her two sisters. He worries that there may be a conflict of interest but dismisses those thoughts as paranoid.
As the investigation into the violent attacks continues, Grant asksfor help from one of his supernatural allies. Ash is a river spirit living near the Folly, and a bit of a party boy, so Grant asks him to keep an eye out for the mysterious woman at the local bars and clubs. That night Ash spots what he calls a Pale Lady, but he is spotted in return and ends up injured. Grant rushes to the scene and saves him but wrecks an ambulance and ends up in the river, causing him a stern talking to from his superiors, who tolerate the magical activities but prefer them to keep a low profile.
In the the house of one of the dead jazzmen they find a pile of books on magic. They track them to Nightingale's old school in Oxford. Grant and Nightingale go visit and get a list of all the books checked out from there, and Grant gets a glimpse into the pre-War days when there were more practicing magicians, before a decline in magical activity during the mid-century.
Grant talks to the head of the Musicians Union, who gives him a lead to another musician that died unexpectedly. He speaks to the man's widow and finds that the man was probably having an affair, the clues suggest it was with a woman in Soho.
As Grant continues digging he discovers some old photos taken after the club was bombed, and spots the same woman he spoke to at the club, looking the same in 1941 as she did the previous night. Grant knows that magic needs an energy source, and that vampires feed off of life energy, and wonders if this is something similar.
Meanwhile the Stephanopolous investigation takes a turn when a retired cop is killed in Norwich. Grant spots a photograph of the jazz club owner there and wonders the two cases are connected. Further investigation reveals that the cop in question was used to work in the Obscene Publications Squad back in the seventies, a notoriously corrupt department.
They bring in the club owner for questioning and he admits to past criminal activity and that the dead cop was involved in some very shady stuff including the sex trade. But he also reveals that he's scared of a new player in town, a magician whose face can't be seen.
The police raid the club and find evidence of sex trafficking and magical activity. While they are busy with that, the Pale Lady shows up at the police station to kill the club owner. Gran chases her out into the streets where they end up in a confrontation and he accidentally kills her.
Following the jazz case Grant goes to speak to one of the river spirits, who also went to Oxford during the same period that the magic books were borrowed. She admits to have noticed a small group of magic practitioners, a group called the Little Crocodiles.
The next day Grant takes Simone to see his father play a gig with his new bandmates, but when Grant's mother sees Simone she attacks her and calls her a witch. A bewildered Simone flees, and when Grant confronts his mother says Simone tried to seduce Lord Grant forty years ago and looked exactly the same then. Grant chases after Simone, when he talks to her he realizes that she has no idea what she is. He tries to make her remember and she is horrified when she realizes how old she is and what must be happening.
Simone runs back home to her sisters and Grant goes to Nightingale. Together they figure out that Simone and her sisters somehow developed a raw magical talent tied to their musical studies in school and instinctively used it to survive the bombing. They've been unwittingly living off of musician's life energies ever since, half ghosts and half vampires.
Knowing Nightingale will try to kill the women Grant goes to warn them before the police arrive, but the Faceless One gets there first, apparently hoping to recruit the women. He and Grant fight on the roof and Grant barely survives until backup arrives, but the Faceless One gets away.
Nightingale thinks they should be found and killed, regardless of whether they know what they did or not. Grant disagrees, saying they have human rights and that as police officers it is their duty to uphold the law, not be executioners. He suggests keeping the sisters in the Folly for safety, like they do with Molly, and Nightingale reluctantly agrees.
However when they finally find them, it is too late, they've committed suicide by taking poison while seated at the same table they would have been at in 1941.
Shaken and depressed Grant goes to visit Lesley, who has had an operation to help her speak a little. The book ends with her revealing a secret to Grant; she has been learning to do magic.
Best part of story, including ending:
The story is a lot of fun and the author manages to keep several interesting lines going from the first book, including the river gods and Grant's interest in codifying the science behind magic. However the plot is a little messy, with a bit too much going on and a lack of clarity as to motivations.
Best scene in story:
When Grant gets Simone to realize what is going on, it's heartbreaking and you feel really bad for both of them.
Opinion about the main character:
Grant is a bit clueless in this one, and its never clear if that's just him or if Simone is somehow clouding his mind so he doesn't notice discrepancies and coincidences.