Enchanted Immortals by C.J. Pinard

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Thomas never thought he would live this long; he expected the usual lifespan of 60 to 70 years. But one terrifying night in 1946 San Francisco has changed all that; he has now been alive 86 years and still looks 20. He and his associates, Jonathan and Kathryn, have been granted Immortality by a group of sylphs belonging to the Zie Council – lead by their queen, Malina – who possess an elixir called Enchantment. But what they and the rest of the Immortals have to do in order to keep receiving this elixir involves protecting sylphs and humans from the faeworlders – vampires and shapeshifters – who want nothing more than to eat, violate, and kill them. For Jonathan, Thomas, and Kathryn, policing the fae is a dirty job, but somebody has to do it. And the payment is eternally priceless.