Reserved for the Cat

Reserved for the Cat (2007) is a novel by American writer Mercedes Lackey, part of her Elemental Masters series. It is set in England and is based on the fairy tale Puss In Boots.
Plot summary.
Ninette Dupond was a dancer with the Paris Opera Ballet who was chosen to be the lead when the prima ballerina Mademoiselle Jean-Marie Augustine is injured. Despite the good reviews her performance receives, she is fired because Augustine becomes jealous of her. Poor and desperate, Ninette is surprised when she finds a tomcat that is able to psychically talk to her. The cat, Thomas, convinces Ninette to migrate to England and become a premier dancer there. With no better options, Ninette takes the chance despite her disbelief in magic.
On the way, Thomas teaches her English, instructs her on the basics of the magical world and convinces her to adopt the identity of the Russian ballerina, Nina Tchereslavsky. Thomas is also able to convince the owner of a music Hall, Nigel Barret, who is an Elemental Master of Air to take 'Nina' on as the main act of his show. In a ploy based on the fairy tale, Nigel and his partners discover Ninette posing as "Nina" supposedly shipwrecked on a beach near Blackpool. Inspired, Nigel and his partners, Arthur (who is in charge of the orchestra) and Wolf (a parrot who supposedly is the reincarnation of Mozart), create a production based on the experience. They set Ninette up in a nice apartment with a maid named Alsie McKenzie (who has no magic, but has the abilities of a Sensitive, which means she can see Elemental beings and the like ) and start rehearsals, with Ninette also doing some dancing acts on the stage in the meantime.
Nigel enlists the help of Elemental Master of Fire and stage magician, Jonathon Hightower, both for the production and that he suspects the shipwrecking was actually an attack on Nina. The threat becomes real, when the real Nina Tchereslavsky discovers Ninette's impersonation. The danger in this is that the real 'Nina' is a rogue dark earth elemental, a troll. This troll possessed the ability to absorb people's identities and their memories. Using the intelligence gained from said absorptions, 'Nina' escaped the bonds of the earth master who summoned her and has been living multiple lives, absorbing many people, and growing in magic power. When 'Nina' discovers Ninette's usurpation of her person, she is furious and vows to destroy the imposter.
The Troll uses many different types of attack, including magical and non-magical to try and destroy Ninette and Nigel's show. Meanwhile, Ninette's latent Talent awakens allowing her to share an emotion connection with her audiences and with Thomas the cat. It is revealed that Thomas is actually Ninette's father, and had been permanently enchanted into the form of a cat by an evil Master prior to Ninette's birth. He had been doing his best to protect his wife and child ever since, but Ninette's mother had died by the time of the events of the book. Eventually Thomas follows a lead back to the Troll's hideout on his own. He gets trapped in the Troll's magic but his emotional distress alerts Ninette to his peril. Ninette goes to rescue Thomas armed with a revolver with bullets crafted to fight evil magic. While Thomas distracts the troll with flattery and praise, Ninette is then able to get close enough to shoot the Troll. However this frees the troll's earth elemental servants who then try to kill Ninette and Thomas. Jonathon arrives to save the day and the burgeoning romance between the two is acknowledged.