Book 3, with spoilers ahead for the earlier ones.
Like, the addition of Gavin to their number.
But as they go through a marsh, Ridmark demonstrates the power of marsh gas to burn, and discusses the way it lures swamp drakes -- and they have to fight one. A trolldomr speaks to them in riddling language, talks of its curiosity about "men of water" (all non-troll species), and tells them about the magic driving the undead.
This leads to an encounter with a young woman who practices wild magic, much to Calliande's horror; being caught outside wards; assassins who wear red masks; the importance of not cheating a dvargir; the death of a young man in a circle of standing stones, and more.