I'm not familiar with the Master Q franchise, but I'm guessing it is squarely aimed at kids. This film is built on the promise of delivering a CG Master Q who interacts with live-action actors. I'm sure that was enough to draw a crowd in Hong Kong, no matter what the actual quality of the film. And beware when watching this, because said quality is truly poor.
Master Q and his friends are running around Hong Kong, looking for a job. When they get a bit too frantic, they cause an accident that involves Fred and Mandy. They lose their memories and become enemies. Master Q feels bad, and he'll do anything to right his wrongs and bring the two back together. This of course is easier said than done.
The CG is very poor, the actors are about as subtle as their CG colleagues (Tse and Cheung can definitely do better) and the comedy is extremely basic. Everything here screams simple filler, hoping to make a buck on the franchise's legacy. It's a bit sad for everyone involved, if you're unfamiliar with Master Q there is no doubt better material available.