Su Yan looks composed enough to belong in a portrait, until her attention catches on some tiny discrepancy and her whole face sharpens. Her skin is warm ivory with a faint olive undertone; her dark violet eyes read almost black in shadow. Silver-brown hair is drawn into a tight coil, pinned with two narrow pieces of bookbinding bone. Her narrow shoulders and long limbs move with careful economy, as if she is always passing between crowded shelves. The cuffs of her ink-blue coat are patched in three different shades of thread, while the glass rose at her throat is polished to an almost unsettling shine. Her fingertips are faintly blue from archival ink, and she habitually turns her hands palm-up before touching anything precious, a surprisingly ceremonial gesture for a working librarian.

Su Yan is meticulous but not cold: she will stop a meeting to correct a date, then quietly cover a student's meal because the correction embarrassed them. When calm, she is dryly funny and invites questions; when frightened, she becomes formal and tries to manage every detail. She wants the truth exposed, yet instinctively withholds it until she believes she can control the consequences.

Su Yan was raised among the lamp galleries of Aerlinis, where her mother repaired vellum and her father copied astronomical tables. At seventy, she was assigned to reconcile the library's ritual index with the records of the neighboring temple. During a storm, a novice named Ko slipped into a sealed reading room to retrieve a record needed to stop a fever outbreak. Su Yan helped her, and the two discovered a set of temple readings that contradicted the official catalog. Su Yan falsified the access log to protect Ko and was promoted to head archivist years later, partly because no one else could explain the catalog's irregularities. Now the magical readings in the library's old glass instruments no longer balance: one line of measurements has begun to drift toward a date that has not happened yet. Su Yan is quietly unsettled and suspects the temple record she once hid is connected. Ko still trusts her as a route into the temple stacks, though Su Yan intends to ask for a dangerous favor in return. Her former mentor, Tesk, believes the discrepancy is ordinary instrument decay and has started auditing her work.