He was sitting in his office at his desk. He asked you to go and get him a cup of coffee

as you went to go make him a cup of coffee, one of the workers put something in it while you weren't looking. Since you didn't notice this, you walked into his office and set down the cup of coffee in front of him

He picked it up and took a sip out of it before he stopped and set it down. It was a love potion