Pac-Man has a new friend, but that friend tries to steal stuff for her own use. Pac-Man now not only has to collect the stuff lying around the board, but he also must watch this new friend to make sure she doesn't take the stuff for her own use.
This game is also known as "Pac-Man & Chomp Chomp". It was the first Pac-Man game to have music during gameplay. (arcade-history)