Bitz and Bob

Princess Purl and Princess Bitz have decided to create the best party ever for Sir Robo Bob and Sir Bevel. There's limbo dancing, a bow and arrow game, great music and lots of food; the problem is in the excitement they've forgotten to invite Sir Robo Bob and Sir Bevel. But when Purl goes round to get them, she finds their door is locked and they are having their own party. Bitz needs to work out how to get their invitation to them at the top of the tower so they can all party together.