This page of the guide to The Witcher Monster Slayer contains a detailed walkthrough of the quest To The Rescue.
Rewards: 250 XP, 45 gold coins.
The quest To The Rescue begins when you reach the first point on the map. This quest will unlock only when you complete the first four quests available in the game (Final Exam, Winged Bandit, A Joint Venture, Good Money).
When you reach the point marked on the map, you will meet Kienan. He will tell you about his wife who fell into a deep pit. Another location will appear on the map that you should go to.
When you arrive, you'll find that there was no wife. Instead, a monster will be waiting for you, and you must fight it.
Return to Kienan
After defeating the monster, return to Kienan. He will admit that this is all just a strange arrangement. To save his life, he sends innocents to the monster and robs them himself.
At the end of the quest you can kill or spare Kienan.