Yep. There’s magic afoot.
Like the unnatural, magic in the setting is a thing of the borderlands, mostly. It’s not taken seriously by the civilized folks of the heartlands, but in the wild, magic can be deadly serious. Magic can ruin crops, make people fall victim to disease, paralyze someone, drive away the vicious spirits of nature and even manipulate the weather.
I’ll remind you again that once the book is in your hands, it’s your game. You can include magic or not, you can make it more central to the setting if you like. It’s your game. Do what you think is fun.
Mechanics-wise, you get magic in two forms: hedge, or folk magic and magical disciplines. Generally speaking, hedge magic is mostly based on ritual and it doesn’t have immediate effects. The effects can be significant, but rarely flashy. Anyone who knows a certain rite can attempt it.
Magical disciplines are more powerful than hedge magic and are more limited in what they can do, since we’ll assume most people never learn more than one, but magical disciplines are what allow flashy and powerful effects. Every magical discipline has tiers in order to represent how much magical mayhem you can unleash , for example the most basic effect of the discipline called Wind-knot allows you to make it rain or snow, while the final tier effect allows you to become a storm and roam the land as a sentient stormcloud. Pretty cool or what? Magical disciplines also allow you to do other cool stuff like control fire, change into a wolf, control spirits and murder people with nightmares.
Of course, sorcerers and other annoying opponents don’t bother with such mechanics. They just have a bunch of abilities they can use when they want. I don’t want you as the gamemaster to worry about representing their abilities in detail.
So, why isn’t the entire Baltic region overrun by nasty sorcerers? Well, first and foremost, it’s rare. Second, it has limits to it. You can’t make yourself invulnerable by magic, for example, and you can’t use healing magic to heal yourself. It just doesn’t work like that. You can’t overcome someone’s free will with magic either: you might trick them but you can’t control anyone’s thoughts. There’s also all sorts of charms and rituals to resist magic which are easier to learn than magic itself, making it possible for even the simplest frontiersman to keep his house safe.
The downside to using magic is that magic is part of the Unnatural. It attracts weird things to you and whatever place you reside at, all in relation to how powerful effects you’re dealing with and how nasty the way of working magic is. When you bless crops by sacrificing some mead, bread and honey, you’re probably OK. If you try to guarantee a season of amazing catches for fishermen by sacrificing ten people, you’re probably going to end up in trouble with all kinds of creatures and phenomena appearing.
Most importantly: magic isn’t science. It’s not bound by any laws except its own laws, it may not work in predictable ways and it always will come with a price, unlike carrying a pistol or a sword.