4.5 Stars for this historical M/M romance set in Victorian-era London. This is the third book in a series and is likely best enjoyed when read in sequence. 
 The first book, AN UNSEEN ATTRACTION, featured the mystery, mischief and murder that befell Clem Tallyfer, bastard son of his Grace, the (late, late) Earl of Moreton as he managed a lodging house, and fell in love with Rowley Green, one of his lodgers. The second book, AN UNNATURAL VICE continues the investigation of whomever killed one of Clem's lodgers, Reverend Lugtrout, and also Clem's half-brother, Edmund, then the earl. Lawyer and journalist Nathanial Roy is working hard for Clem to ensure he doesn't get put out of his lodging house by his uncle, an mean elderly man who is claiming the title as Edmund had no legal offspring. But spiritualist Justin Lazarus met Edmund's secret wife, and knows a son was born. They spend most of their book on the run from London's killer fog, and a real-live killer, while they hunt down the rightful Earl of Moreton. 
 We already know the identity of the apparent earl by the end of the second book, and he's not what anyone expected. Pen, and his twin Greta, christened Repentance and Regret after being born in a religious sect where their mother took refuge when her scoundrel of a husband married her, had his merry way, and discarded her at the age of 16, are now performers. And Pen likes it that way. He and Greta have a good life where Pen can allow some room for his...unusual and generally unacceptable behavior. 
 See, Pen is gender dysmorphic. He's not happy in men's clothes all the time, and he's also not happy in women's clothes either. He has long, lush hair, and often paints his face to match that of Greta-and not only for their performances. There are days he can't bear to look as his naked form, and his broad, strong hands-tools of his trade-horrify him in their masculinity. In the musical hall, he can dress in ways that are counter to society's dictates and pass it off as a lark, or the eccentricity of a performer. And he likes it too much to give up for some stuffy title. There's no way he could mask his nature for the twenty-or fifty-years he'd need to as an earl. And the idea of marrying a woman to sire an heir? *Pen shudders* 
 Mark Braglewicz was born to a Polish anarchist, and endured life with only one arm. He's an enquiry agent, what you might call a private investigator in today's terms. His dear friends Clem and Nathaniel need his help tracking down the missing twins, and there's no shortage of death and destruction that follows this search. Already three men are dead, and two properties were either burned or vandalized. It's actually not hard for Mark to find Pen, nor is it hard to woo him. Pen hasn't found a man before who had such flexibility in his desires. Mark finds Pen's gender-bending appeals to him far too much, and he's in a bad spot. He's falling for Pen, but the murderer is still on the loose. It's with no other choice than to save his friends and protect Pen from the murderer that he reveals Pen to be the rightful Earl of Moreton. 
 Pen is furious at the betrayal. And he's not happy with the process of investigation. As his great-uncle and cousin dispute the situation, Pen and Greta are sent to pass the time at the family seat in the country. With their new "relations." It's uncomfortable, and unnerving, for Pen to be scrutinized so. Clem and his half-cousin Tim, also make the journey and they are good companions. Greta seems so happy on her walks with Tim, and Pen can't escape his title, though he desperately wants to do so. Once the lawyers finish their investigation, he'll be sealed into the title forever. And, man, is he mad with Mark for this burden! 
 Though, it wasn't Mark's fault. It was his rotten father's fault. If Pen is destined to be this earl, then he's going to make things right within this whole dysfunctional family, by golly! Well, if he lives that long. It's clear the danger didn't remain behind in London, and Pen's fears that he's being stalked are only assuaged when Mark turns up at the country estate to search for a possible killer among the house staff and visitors. And, Mark's able to win back his beloved Pen. 
 The mystery was, as in the previous books, slowly revealed and had a great twist. The open love between Mark and Pen is tender and thoughtful. I could see why both men were so conflicted. If Pen is a earl, Mark has no hope of sharing any sort of love, clandestine or not, with him. But, the story ends happy-and realistically so. Pen is a quick thinker, and when his chance appears to make his life as he sees fit, he grasps that lifeline with both his strong hands and runs like the devil chased him. This is a fantastic mystery-romance series with just the right amount of intrigue and affection and a beautifully-rendered historical setting.