Coulaine is the proprietor of Keys and Bolts, a locksmithying shop in Ticoro. He made the lock to the City Ramparts and provided locks to many Ticoran residents and businesses, and is influential in the local Guild. He despises puzzle locks such as those on lever and bead chests, priding himself on crafting unpickable locks for his customers.
After apprenticing Torrence Pasege, Coulaine held him back from an overdue journeyman promotion and took credit for his skillful work. When Torrence caught and confronted him about accepting compliments for a lock Torrence had made, Coulaine threw him out, unconcerned that the black mark of being dismissed by his master would make it impossible to apprentice with someone else.
During the Spring Festival, Coulaine ran a special on chastity belts, but was aggravated by reports that locks he'd installed in Ticoro were being systemically picked.
If the party asks him for a key to the Ramparts, he refuses at first, but then agrees to trade it for the name of the person picking his locks. After learning the story from the culprit, Torrence Pasege, they can return and convince him not to turn Torrence over to the constable; he hasn't stolen anything and probably wouldn't be jailed, while the news that Coulaine's locks were pickable would get out and Torrence might even teach his secrets to a new master. With that in mind, along with the workload at the shop (more than enough for two), Coulaine gives them the key and agrees to take Torrence back on, noting that as his master he can find a way to collect for the trouble Torrence has given him.