The quest for eternal life is a fictional trope that just won’t die, despite the fact that endless days might, in the very long run, turn out to be a mixed blessing. Think of Tithonus withering away because Aurora forgot to add eternal youth when she secured immortality for him. Former CIA intelligence analyst Alma Katsu takes on this theme in her first novel, “The Taker,” an ambitious if derivative tale of romantic obsession that spans centuries.

It’s hard not to be derivative with a subject that was first explored in Gilgamesh, millennia ago. Katsu’s story doesn’t extend back quite that far. It opens in a small-town emergency room in contemporary Maine, where Luke Findley, the doctor on call, arrives in the middle of a wintry night to examine a disorderly woman who’s been brought in by the local constabulary.

“He’s expecting a big, mannish biker woman, red-faced and with a split lip, and is surprised to see that the woman is small and young. She could be a teenager. Slender and boyish except for the pretty face and mass of yellow corkscrew curls, a cherub’s hair.”

The sheriff quickly advises Luke that looks are deceptive. “That girl is a killer. She told us she stabbed a man to death and left his body out in the woods.”

The girl’s apparent age is deceptive, too, as Luke finds out when he’s alone with her in the examining room: She grabs a scalpel, slashes herself and waits as the horror-stricken Luke watches her bleeding rib cage knit itself back together. Then the girl, Lanny, begins to recount her history, starting in 1809, when she fell in love with Jonathan St. Andrew, scion of the family that gave the town its name.

“The Taker: A Novel” by Alma Katsu. (Gallery Books)

Lanny isn’t alone in her infatuation. Jonathan is one of those young men, beloved of romantic novelists, who seems to have wandered in from a Gap ad. He’s “uncommon . . . exceptionally clever, exceptionally strong, exceptionally healthy, and above all, exceptionally beautiful . . . a wonder . . . perfection . . . brilliant and intoxicating” And so on. Jonathan’s a few years older than Lanny, but that doesn’t stop her from throwing herself at him when he’s only 14. The two are forcibly separated only later, when Lanny finds herself pregnant and Jonathan is betrothed to another.

Sent away to a convent in Boston, she meets up with a trio of slumming aristos swanning around the city in a fancy carriage. The guileless Lanny is promptly whisked off to their den of iniquity, complete with a sloe-eyed, midget odalisque. This menage is presided over by the sinister Adair, an opium-puffing Hungarian count who seduces Lanny and indoctrinates her into the secret that binds his unhappy household: an elixir that confers eternal life. But the truth behind the elixir and its master is much darker than Lanny can imagine.

In spite of its potboiler elements, “The Taker” takes a while to develop a head of steam. The narrative loses momentum as it switches between Lanny’s account of her centuries-old trials and the lackluster, present-day romance that ensues between her and Luke. Also, Katsu’s prose tends toward the infelicitous — “A complete dread chill seized me.” “Paralytic with fear, she didn’t move.” And for too many pages, “The Taker” seems a mere patchwork of other novels: the thwarted Scarlett-Ashley romance from “Gone With the Wind”; the dysfunctional supernatural family dynamic in Anne Rice’s “Vampire Chronicles”; plot turns (and a name) borrowed from Edgar Allan Poe.

But when Adair recounts his own disturbing history in medieval Europe, the novel begins to soar and stays aloft until its denouement. Then the uncanny meaning of its title becomes clear, and “The Taker” finally delivers a grimly satisying new twist to a very old tale.

Hand’s thriller “Available Dark” will be out in February.

THE TAKER

By Alma Katsu

Gallery. 438 pp. $25