"Someone Else Is Steppin' In (Slippin' Out, Slippin' In)" is a blues song by Buddy Guy. The lyrics depict a story of betrayal and infidelity in a relationship. The narrator comes home one morning to find that their key no longer fits the lock, indicating that their partner has changed the locks or moved out. They express their shock and realization that their partner has been cheating on them while they were unaware. The narrator feels like a fool for trusting their partner and being there for them when nobody else was around. However, they have now discovered a new friend or lover who has entered their life while their partner was slipping out. The narrator's heartbreak and anger are evident as they tell their partner to go back to where they've been, implying that the relationship is over. The song's chorus emphasizes the narrator's newfound independence and confidence. They proclaim that their partner doesn't mean anything to them anymore and that they have become a brand new person. The lyrics mention a new way of walking and wearing their hair, symbolizing a change in appearance and attitude. The repeated line, "This big smile on my face, baby, you didn't put it there," highlights the narrator's assertion that their happiness is no longer dependent on their unfaithful partner. They have moved on from the pain and are embracing a fresh start without them. Overall, "Someone Else Is Steppin' In (Slippin' Out, Slippin' In)" is a bluesy anthem about overcoming a betrayal and finding strength in moving on from a toxic relationship.