Stellarlune (keeper of the Lost Cities, #9)

The ninth installment in Shannon Messenger's Keeper of the Lost Cities series, a middle-grade fantasy set in hidden elvin cities, follows Sophie Foster, a teenage girl genetically engineered by a secret organization called the Black Swan. Sophie possesses more special abilities than any elf in history: telepathy, inflicting (projecting emotions as weapons), enhancing (boosting others' powers through touch), telekinesis, and teleporting. She and her friends have spent years battling the Neverseen, an elvin rebel group seeking to overthrow the ruling Council. The story begins immediately after Sophie burned down one of the Neverseen's storehouses.

Sophie returns home to Havenfield, the estate she shares with her adoptive parents Grady and Edaline, to find a goodbye note from Keefe Sencen. Keefe is an Empath whose mother, Lady Gisela, a leader of the Neverseen, subjected him to a dangerous ritual in an underground dwarven city called Loamnore that triggered frightening new powers, including irresistible voice commands. His note explains he is too dangerous to remain in the Lost Cities and plans to hide among humans. Grady admits he watched Keefe leap away using a pathfinder, a crystal used for teleportation, set to a random human destination.

Sophie's friend Dex Dizznee, a gifted Technopath (someone who manipulates technology with his mind), reveals that Keefe has also manifested the ability to sense and potentially trigger others' special abilities. Seeking further clues, Sophie visits Lord Cassius, Keefe's estranged father, and enters his mind telepathically. She uncovers a memory Lady Gisela tried to erase, revealing that Gisela is secretly a Conjurer (able to summon and move objects through an invisible void), has been studying natural forces like star alignments and the Prime Sources (sunlight, moonlight, starlight), and designed a plan called stellarlune as a three-step process. The first step involved elixirs given to Cassius; the second was the ritual in Loamnore; the third remains unknown. Gisela also mentions something called "Elysian," which Cassius does not recognize. He suggests Gisela may be the only one who can help Keefe function and control his new abilities.

Sophie contacts her human sister Amy, who mentions three uninhabited islands that recently vanished in mysterious tsunamis, a detail Sophie flags for later. Meanwhile, Sophie's friends confront Glimmer, a former Neverseen member living under guard. Glimmer admits she freed Lady Gisela from shadow bonds, restraints woven from shadows, during the battle in Loamnore. She reveals her identity as Rayni Aria, whose parents were banished for manipulating the elvin matchmaking system. Rayni proposes arranging a meeting with Trix, the Neverseen's Guster (wind controller), who might switch sides now that his partner Umber is dead. Wylie Endal, one of Sophie's allies, insists the Council must approve any such meeting.

Sophie and Dex visit Councillor Oralie, Sophie's secret biological mother, to open Kenric's cache, a device where former Councillor Kenric stored seven "Forgotten Secrets," memories deemed too dangerous to retain. The key revelations: Kenric investigated stellarlune and Elysian years earlier; he once brought Oralie to an unmapped location with a river whose rushing water sounded like a quiet trickle, silent crumpled-leaf trees, and a strange "awareness" permeating the landscape; and the final memory contains a hand-drawn map of five converging lines around a star-shaped marker with an ancient rune. Sophie recognizes the image because the Black Swan planted a nearly identical one in her mind years ago.

Sophie's ogre companion Ro identifies the lines as rivers, and Edaline translates the rune as "E." Sophie concludes the map marks Elysian, a hidden place at the intersection of five rivers where the Ancient Council concealed a power source. She attempts to teleport there but slams against an invisible barrier. Mr. Forkle, the Black Swan's leader, warns Sophie against letting concern for Keefe narrow her focus. He reveals that troll treaty negotiations have collapsed and that Cadfael, a rebel ogre, may be planning an uprising. He pressures Ro to warn her father, King Dimitar. Ro agrees and departs for ogre territory, first giving Sophie a dagger and telling her that Keefe's feelings for her are genuine.

Mr. Forkle announces that Foxfire, the elvin academy, is reopening, and that the Neverseen have retaliated for the storehouse fire by destroying Brumevale, an ancient Black Swan lighthouse, with an unknown explosive weapon. At school, Tiergan, Sophie's trainer, determines that her Cognate bond with Fitz Vacker—a specialized, power-amplifying telepathic pairing—is near collapse and initiates a "Cognate Inquisition," a process requiring radical honesty between telepathic partners. The exercise reveals Fitz's resentment about Sophie's role as leader, his discomfort with her unmatchable status (a social designation that makes romance politically fraught among elves), and Sophie's intensely strong reaction when Fitz mentions Keefe. Despite the difficulty, the process increases their combined mental power.

The Council approves the meeting with Trix. At a remote bluff, Trix arrives accompanied by a portable illusion of Vespera, an Ancient elvin criminal who now controls the Neverseen. Vespera reveals that Lady Gisela has split from the Neverseen and may be behind both the troll crisis and Brumevale's destruction. She explains stellarlune's final component: during a rare alignment called "Nightfall," a sixth unmapped star appears for twelve days, and its light imbues special rocks in Elysian's hidden quarry with the combined power of all three Prime Sources. After Vespera departs, Trix reveals that Gisela can track Keefe through shadowflux, a shadow-based substance secretly implanted in Keefe's heart, creating a detectable "ripple" twice daily. Sophie refuses the alliance but keeps the intelligence.

Dex modifies Sophie's Spyball, a scrying device, to detect the ripple, tracking Keefe to London. Sophie teleports there with Dex and Tam, one of Sophie's allies and a Shade (shadow manipulator). They find Keefe in a luxury hotel, surviving on money from stolen jewelry. Tam extracts the shadowflux using Sophie's enhancing. Keefe insists the Elysian power source must be destroyed and returns to the Lost Cities.

Keefe begins daily ability training with Grady, whose experience controlling his own mesmerizing, a difficult mind-influencing power, makes him a suitable mentor. Keefe confesses his empathy has gone numb from blocking overwhelming emotions. After days of failed attempts, Sophie finally tells Keefe she cares about him as more than a friend. He admits he has wanted this since they met, and they kiss.

Fitz arrives with urgent news: a hidden path in Wylie's subconscious requires a stronger Cognate bond to breach. Sophie and Fitz complete the final step of their Inquisition. Sophie tells Fitz she likes Keefe and that they kissed. Fitz is devastated, but their honesty pushes their joint power above 1,000 for the first time. They enter Wylie's mind and find a hidden message from his murdered mother, Cyrah, who reveals she hid Lady Gisela's starstone, a special crystal programmed to teleport its user to a specific location, inside one of her original hair comb designs and sent it "somewhere safe." Biana Vacker, Fitz's sister, recognizes the design from combs Cyrah once sold to Biana's father. One stone flashes blue, confirming it is a starstone.

Sophie rallies the group and leaps to Elysian using the starstone but finds only inert hills and rocks after an all-night search. When Vespera's illusion later appears demanding the starstone, Sophie assembles a team and returns. Vespera dissolves her layered illusions to reveal a quarry wrapped in vines of Noxflares, fire-reactive plants created by the Ancient Council. The rocks appear powerless until Marella, one of Sophie's friends and a Pyrokinetic (fire controller), realizes the Noxflares must be burned in specific layered colored flames, replicating a pattern that imprisoned former Councillor Fintan demonstrated in his cache memory. The fire erupts brilliantly, and Sophie holds up Dex's Illusion Breaker, dissolving all remaining illusions to reveal Elysian enclosed within a massive dome of stained glass.

Lady Gisela appears with mutant trolls that capture Sandor, Sophie's goblin bodyguard. She reveals she brokered the troll alliance by offering Empress Pernille, the troll ruler, the vanished human islands. She kills Vespera by conjuring an explosive crystal shard. Sophie and her friends fight back, but all abilities suddenly shut off. A cloaked figure steps out of thin air and announces, "My name is Elysian. And I am the power source you're all here looking for."

The story ends on this cliffhanger, with the nature of Elysian and the confrontation with Gisela unresolved. A bonus scene from Marella's perspective reveals that Fintan offered her a secret bargain: if she discovers what is "missing" from the Noxflares, he will open his remaining cache memories and reveal the truth about her mother's disabling "accident," implying it was not accidental. Marella keeps the offer to herself.