Exchange the Role of Guest for that of Host
Defeat the enemy from within by infiltrating the enemy's camp under the guise of cooperation, surrender, or peace treaties. In this way you can discover his weakness and then, when the enemy's guard is relaxed, strike directly at the source of his strength.
She wasn't my boss, but I did a lot of work for her. She even got one of my previous supervisors fired. She wasn't very good at her job, but she had been a holy terror for a long time because she was having an affair with a senior executive. Of course, I did whatever she said. To her face. Behind her back, I fed anything negative about her to my boss and boss' peers, each one of with whom I took pains to get on good terms. In turn, I (indirectly and obliquely) found out information from them about the executive with whom she was having an affair... and even went so far as to cultivate a friendship with him... This mitigated the amount of damage she was able to do to me. Once the company got bought out, I was well positioned... and she was fired. The senior executive with whom she'd been having the affair took his stock, cashed it out for a huge profit, and went back to his wife. It's nice, sometimes, the way the Benjamin's make your decisions for you!