The Darkest Angel is part of the Heart of Darkness anthology with Susan Krinard and Maggie Shayne.

Lords of the Underworld tale
An iron-willed demon assassin, the angel Lysander has never known lust—until he meets Bianka. Spawned from the bloodline of Lucifer, the beautiful but deadly Harpy is determined to lead the pure-hearted Lysander into temptation…

Title: The Darkest Angel
Author: Gena Showalter
Series: Lords of the Underworld, book 4.5
Genre: Paranormal Romance
Publisher: HQN
Year of release: 2010 (January)
Format: Mass Market Paperback
Source: Bought via The Bookdepository
First line: From high in the heavens, Lysander spotted his prey.

QnD-review:
Hero: Lysander is an angel, a soldier for the One True Deity and one of the Elite Seven. He’s a virgin, which makes him come across innocently cute, had the feeling even though he’s a badass warrior angel, he was a little scared of Bianka, or rather of his feelings for Bianka. He craves her but fights the temptations as hard as he can. Couldn't quite put my finger on Lysander's character. He stayed on the fringes of elusiveness for me.
Heroine: Bianka Skyhawk is the daughter of a Harpy and a phoenix shapeshifter. (witty, outspoken, confident, bold)
Plot: There's a flimsy plot about Bianka being the ultimate temptation and downfall for Lysander and him keeping her captive to convert her to the godly ways and if she doesn't he will have to kill her. Primarily I felt this to be a set up story for Aeron’s story whose heroine makes her appearance in this novella, and I am anxiously looking forward to it.
Writing: Though short, this novella is filled with Gena Showalter’s trademark humor, internal cravings and scorching sensuality.
Likes: Loved the oil-wrestling scene! And I was also intrigued by the set-up for Aeron's story, this is going to be interesting to say the least.
Dislikes: Again the length of the story! I wanted to read more about Lysander and Bianka and I wanted more of a plot. Also there was a lot of information and world building in the first few pages. I can imagine that for readers unknown to the series this is great because it makes the novella more stand alone, but for followers of the series it's unnecessary and felt repetitive.
Verdict: The wrap-up felt a bit rushed but with a 140 page novella that’s not strange. And even though I am not a fan of anthology length novellas, my favorite authors rarely let me down in them. Showalter proved this once again with THE DARKEST ANGEL which I enjoyed but primarily for the oil-wrestling scene and the set-up for Aeron's story: THE DARKEST PASSION.
Rating: 7.0 out of 10