Despite the fishy nature of the mission description, Jack wants you to go check on his grandmother. You will notice the optional objective of picking five flowers, all of which are on the path leading to the grandmother’s house, so they are pretty hard to miss (plus they’re all marked on your map). When you approach the house, a bunch of bandits will attack, so head inside (through the back) and then a Goliath will drop down to your surprise. Kill him, then check on the grandmother, who is already dead, picking up her buzz axe and returning to turn in the mission.

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You'll find the flowers on the path to the house (left). Be careful of the Goliath that drops down inside the house (right).