Nan and Sarah aren't masters of magic like the central characters in the other books. Instead, their skills have a slightly different flavor. As a psychic, Nan can not only read minds, but she can touch objects and learn their history. Also, at times of need, it seems that a past life takes over and she becomes a Celtic warrior with an impressive amount of battle knowledge. Meanwhile, Sarah, a medium, can communicate with spirits and help guide them to the other side so they can be at peace, or, if necessary, get them pulled into a much darker direction so they can pay for their crimes. The women are also accompanied by a pair of familiars. Nan has a raven named Neville, while Sarah's is parrot named Grey. Both birds are intelligent, speak, and have a sense for magic that will come in handy many times in A Study in Sable.
While Nan and Sarah aren't themselves wizards, the people they are sent to London to help are. Dr. John Watson and his wife Mary have a secret that was never pointed out in Sir Arthur Conan Doyle's books about Sherlock Holmes (mainly because Watson has made it clear to Doyle that he wants it kept quiet). The doctor is a Water Master and Mary is an Air Master. With these abilities, the two Watsons help to solve the cases that Sherlock turns his nose up at, claiming them to be just superstition. Nan and Sarah are sent to the Watsons in order to help them in their endeavors, especially since an old foe of the ladies has started to make its presence known again.
Number 10 Berkeley Square is a house that Nan and Sarah barely escaped from when they were young. The presence in the house has a history of killing anyone that riles it up, and while the two girls got away, they didn't stop it from drawing in more victims over the years. The first mission the Watsons, Nan and Sarah go on is to finally put an end to whatever lurks in that house's dark places. They will need help, research and a lot of magical knowledge to solve this problem, but this mission is just a preamble to a much bigger plot, one that actually touches heavily on Sherlock's own current case of a missing woman.
When the missing woman's sister, a German opera singer, contacts Sarah in the hopes of putting the ghosts that are tormenting the diva's sleep to rest, the opportunity to not only help the spirits but also learn more about the woman in order to help Sherlock's case is too much to ignore. Sarah quickly learns that the ghosts that inhabit the old hotel the woman is staying in show up at her suite each night and keep the singer up, to the detriment of the woman's career. Sarah tasks herself with working with each spirit one-on-one in order to help them move on, but as she does so, she finds some of the specters are harder to handle than others.
Meanwhile, Nan continues to work directly with the Watsons, and even Sherlock, on a couple of cases, but she starts to notice some changes in Sarah's behavior. Is it because of the long nights? Maybe it's the pampering that the singer gives the psychic? Or could it be something more sinister? Regardless, one thing quickly becomes apparent, the first case that the girls work independently of each other will put strain on, and strongly test, their friendship.
I have to confess, I haven't read any of the other Elemental Masters novels. What I've learned about the rest of the series, and about Nan and Sarah's previous adventures, has been gleaned off of internet research, but the mostly one-off story nature of the series makes it one that you can pretty much jump in at any point without missing much. While Nan and Sarah already have a backstory built up, I found that it didn't keep me from enjoying A Study in Sable, I just had to realize there were some bits of their history that I didn't know the details. When one of those details became necessary, Lackey easily weaves in the required knowledge so that I never felt like some ability or information came out of nowhere.
A Study in Sable has piqued my interest enough to look into the other books in the series, especially A Wizard of London where Sarah and Nan are first introduced. So whether you are an avid follower of Elemental Masters, or the idea of Watson's role as a paranormal investigator picking up the cases Sherlock doesn't want to fool with intrigues you (as it did me), you should find plenty to enjoy in this novel.