Thorn's charcoal-brown skin has a faint, pebbled sheen, like river stone after rain. Two small pairs of horns curl close to her skull, one pair above the temples and a shorter pair behind them. Her acid-green mohawk stands in stiff, uneven bristles, and her eyes look like dark panes of glass shattered into many fine facets. She blinks sideways, one lid sliding across each eye like a lizard's. She moves with a gardener's careful economy, then snaps into unnerving speed when threatened. Her prehensile tail resembles a living thorn whip, a cord of green-black vine with tiny hooked barbs; she usually coils it beneath her long coat. A surprising detail is that she keeps a small, neatly folded cloth in her pocket for wiping soil from other people's shoes, even when she has just threatened them.

Thorn is quick-witted and mildly sadistic, especially when she has the upper hand, yet she has a patient tenderness for seedlings, sick animals, and people who admit they are frightened. In a calm mood she makes others laugh while quietly measuring their motives. Under pressure she becomes brisk and unsentimental, though guilt can make her reckless when someone vulnerable is at stake.

Thorn was raised alongside her sister, Cassie Everbloom, but found her own footing early in the dangerous work of an assassin's apprentice. The training taught her to read a room by its breath, smell bitter compounds on a blade, and wait without fidgeting. It also made her think of people as problems that could be removed. That changed during an assignment in which she was ordered to poison a wounded target who had already surrendered. Thorn hesitated long enough for the target to die from their injuries anyway, and the memory of that needless choice lodged in her more deeply than any lesson from her trainer. She left the trade with a stolen bundle of seeds and a distrust of anyone who calls killing clean work. Now she tends the garden for the Beetle Juice Apothecary, raising medicinal and toxic plants in the same cramped beds. She is quick-witted, useful, and not entirely safe to cross. Cassie serves as a battle priestess acolyte of the Silver Hearth Church; the sisters care for one another, but their different answers to violence keep their conversations sharp. Thorn's current problems include a dwindling stock of rare seeds, old contacts who still expect her to finish unfinished business, and the temptation to treat her garden's poison as a substitute for difficult conversations.