In the Lion's Mouth is the third book in Michael Flynn's science fiction series that began with The January Dancer and was followed by Up Jim River. I'd recommend reading those before reading this one; it's not strictly necessary in order to understand what's going on during In the Lion's Mouth, but it certainly helps.
In the far future, humanity is spread across countless worlds dominated by two great powers in a centuries-long cold war, the despotic Confederation of central worlds and loose alliance that opposes it called the United league of the periphery. Donovan buigh was once a Shadow, an agent of the confederation's elite intelligence service- before he was subjected to experimental mind altering-procedure that was supposed to create a single man with the skills and expertise of an entire team of experts but instead left him with huge gaps in his memory and a fragmented mind split between multiple quarreling personalities. He ended up in the Periphery, a broken man quietly drinking himself into his grave until he found himself drawn back into the long struggle between the and Confederation and league, now defending his new home from the machinations of the Confederation and it's rulers, the mysterious oligarchs known only as Those of Name.
He has finally started to gain a measure of peace and purpose in his new life when he finds himself forced back into the old one by a Confederate agent he met decades before (during The Januaryy Dancer), Ravn Olafsdottr. She abducts Donovan and smuggles him back into the Confederation- but not on behalf of Those of Name. The Shadows are wracked by an internal struggle between those loyal to Those of Name and those who now seek to overthrow them, and the latter want Donovan- less for who he is than for who he used to be, in the long empty gaps of his memory. Donovan eventually agrees to join them, putting him on a collision course with some of the deadliest killers in the galaxy, the truth about his own identity, and Those of Name themselves.
In the Lion's Mouth is a highly enjoyable book and a fine continuation of the series that started with The January Dancer. I loved the central characters Donovan buigh and Ravn Olafsdottr, and the plot is interesting and exciting. There are a number of well-done action scenes, and Flynn's talent for description in general is again in evidence.
The framing device of the book is that the story is being told by Ravn Olafsdottr, who has snuck back into the League after the main events of the book to bring Donovan's story to Bridget ban, a long-time veteran of the League's own intelligence service, who has spent her life on the opposite side of the long cold war between the two great powers, and her daughter with Donovan, Mearana. This proves to very effective, both because it provides a different viewpoint from the previous books in the series and because of the atmosphere it creates when the book occasionally shifts from the main narrative back to the frame story. The tension of the interactions between two lifelong enemies sharing a brief truce and the stress and anxiety of Bridget ban and her daughter as Ravn tells herstory - and mockingly refuses to reveal ahead of time if Donovan will be alive or dead at the end of it- are palpable, and this adds a lot.
My one initial disappointment with In the Lion's Mouth was that it is relatively constrained in scope, focusing on just a few worlds. Consequently, it doesn't have the same variety and epic sense of scale as its predecessors, which took the reader all the periphery and beyond. In the Lion's Mouth, by contrast, is relatively modest in scope, concentrating on a few planets. I say “initial” because once I had adjusted to it I thought it worked quite well for the sort of story the author is telling here, and Flynn shows that he can still do a good story in this setting while working on a more constrained scale. The narrower scope of the main story also fits well thematically with the setting, adding to the contrast between the despotic Confederation and the freewheeling diversity of the League, and complements the claustrophobic anxiety of the frame story.
I highly recommend In the Lion's Mouth for space opera fans, though I would encourage people who haven't read The January Dancer and Up Jim River to do so first. The entire series is well-worth getting into.