Lady Scarlet was interested in dominating her stubborn slave because she wanted him to learn never to do things that way. The mistress felt that the best way to deal with him was to do something to shock him to the core so she came home with a man and she had the slave lick their feet as they made out and had fun. He was humiliated and his ego deflated.
Lady Scarlet is the sort of person who does not take things lying down and that is what she did to this loser. The mistress made sure that this loser learned his lesson cruelly by turning him into a foot slave. He had to lick her dirty feet and also suck her toes. She told him that he would soon be ball busted if he did not change and he did out of fear.