This book does have a moral — travel along a wall long enough and you will eventually come to a door. Robin's wall is his crippled condition, but he maintains a good attitude and trains in those skills he can manage. When his door comes, he's ready for it.

But mostly, it was a good old-fashioned kids' adventure story. The plot was exciting and the characters were likeable. The writing was a bit simplistic, and there were some plot holes, but so what.