After hearing about a monster that lived in the Unsterbliche Sumpf and kills people there, the heros investigate. They talk to a number of people - the priest of the Vaticine Church in Sieger, a Highland mercenary who settled in Eisen after the war, various people they meet in the tavern. Everything points to a kelpie - not a native Eisen monster.
After trying to lure the Kelpie with blood and dried meat and trying to flush it by throwing stones into the bog, they decide to let Lina get drunk and wander through the bog alone - everyone else who was taken had been alone, too. That works and the Kelpie makes an appearance. For a short moment, it's the most beautiful horse Lina has ever seen and she comes very close to touching it, but her aversion to horses kickstarts her brain just in time.
Everyone attacks while Mateo confuses the horse by dancing. Both Lina and Jimmy get stuck to the horse at some point, Elaisa manages to throw a halter over its head and Lina freezes the bog, getting the Kelpie stuck in the ice.
Before they can kill it, a woman comes running and puts herself between them and the horse. She introduces herself as Solveig and tells them that she is the local witch. She has some degree of control over the Kelpie. It keeps the bog free of monsters that would be even worse and definitely not controlled by the witch. The heroes are not exactly happy with this, but on the other hand: this is Eisen and things are never perfect here. They come to an agreement: Solveig will teach the locals to hunt and kill monsters. This would be, in a better world, the job of the king and paid monster hunters, but that won't happen in the foreseeable future. So for now, Solveig helps the people to help themselves and if at one point, someone kills the Kelpie, she won't try to stop them.