Eoin Colfer

When fourteen-year-old genius Artemis Fowl realizes that the only cure for his mother’s case of Spelltropy lies in a species of lemur that Artemis made extinct eight years ago, there is only one solution: Grab your 80-year-old, elfin-police-captain-friend Holly Short and trick her into traveling back in time to stop your formerly evil, ten-year-old self from killing off the last of the all-cure lemurs.

Author Eoin Colfer does a masterful job presenting a single nonbranching, static timeline, complete with three consistent causal loops (further described in our tag notes for this story). But really, Eoin, you missed the shuttle on “the kiss”! With the help of N°1, Artemis can time travel, so if you're intent on his first romantic kiss coming from Holly Short, couldn’t N°1 have brought Holly’s actual fourteen-year-old self into the story? Might have even presented an opportunity for a fourth causal loop: Fourteen-year-old Holly kissees fourteen-year-old Artemis, but only because fifteen-year-old Artemis had already told thirteen-year-old Holly that they would enjoy it. —Michael Main

When fourteen-year-old Victorian waif Riley shows up in the 21st century on seventeen-year-old FBI Agent Chevie Savano’s watch, the two of them pair up and head back to the late 19th century to escape Riley’s evil pursuer.

Although the book involves wormholes and scientists, it’s really a quantum fantasy, wherein an ordinary fantasy has the word “quantum” scattered throughout in key places, typically before the word magic, magician, or wormhole. Nevertheless, we’ve listed it as science fiction to match its publicity material. —Michael Main