The Kayran is a Witcher 2 main quest which must be completed in order to advance through the games story.
When you celebrate inside the tavern with Triss, Roche, Zoltan and Dandelion a citizen rushes in yelling that a monster (The Kayran) appeared in the port.
We follow the citizen, but when we arrive, the monster is gone; however on the docks we meet a new character, a sorceress named Sile de Tansarville.
Seems that during the attack, a villager named Sosek, was injured. His comrades blame Sile de Tansarville for this unfortunate event.
At this point, you can choose to persuade the peasants and send them away nicely, or you can find additional information and convince the villagers that the Kayran is responsible for Soseks wounds.
No matter how we play this part, the villagers will disperse and we remain with Triss and Sile de Tansarville, who informs us that she came to Flotsam when she heard that about the Kayran.
During the dialogue, we can observe that Sile and Triss hate each other.
A new character, named Louis Merse, interrupts the dialogue, stating that a trader offers a reward to those who manage to kill the Kayran.
Sile offers her services claiming that all she needs are some ingredients from the monsters corpse. She also tells us that we should talk to Louis Merse again. If we need her, we can find her at the tavern.
The Kayran main quest continues, but to advance we have to focus on The Kayran: A Matter of Price.