Devastating Sorrow (Penny Montague, Book 1‪)‬

Witch and ex-military, Penny Montague is sick of her immortal life. Working as a phone sex operator to occupy her time and keep in touch with her humanity, she spends her days trying to find a way to end her long, lonely existence and her nights pretending to care about men with mommy issues, strange fantasies, and twisted imaginations.
Life wasn't always this bad though. When Penny's ninety-two year old son, Charlie, dies in her arms the crushing reality of her long life truly hits her. What else is there to live for without her son? She's ready to give it all up, and has tried multiple times, when her brother, Byron, shows up on her doorstep, trouble on his tail as always. It wasn't until armed guards burst into her home, drag her from her bed, and throw them both into the dungeons of Midnight Manor that Penny realizes this is much worse than Byron's normal scheming.
Midnight Manor is the control center of all immortals, run by an elite group called The Elders' Court. Nothing happens in the world without Midnight Manor having their fingers in the pot. They raise and educate immortal children from an early age and place them throughout the world in positions beneficial to their causes, both present and future. There isn't anything that happens, be it war, arms trades, or scientific achievement, that Midnight Manor doesn't influence.
Penny retired from the Midnight Manor military nearly a century before, but now, in order to save her brother from being tortured for the rest of his immortal life because he slept with the wrong man's wife, The Elders' Court gives Penny the choice to hunt down and return a runaway scientist or risk a fate worse than death and join her brother in the torture chambers for eternity.
Penny, with the help of a few people from her past, decides to at least attempt the retrieval. After all, according to The Elders' Court, the scientist is a danger to all immortals and his research must be returned. Tracking was her specialty during her time in the service.
This should be an easy in and out kind of mission with only a couple of days of work involved. Right?