Step 1: Understanding the Concept:
This question asks about a specific action taken by the main character, Griffin, in the story "Footprints without Feet." It concerns the event that made him a homeless wanderer.
Step 2: Detailed Explanation:
The story explains that Griffin was a brilliant but lawless scientist. His landlord disliked him and tried to evict him. In revenge, Griffin, who had already made himself invisible, took action. The text states: "In revenge Griffin set fire to the house." This act forced him to remove his clothes to become unseen and flee into the cold London air.
Step 3: Final Answer:
In revenge against his landlord, Griffin set fire to the house.