The wall panel is located at Kenny Crow's house. It is a slidable panel that hides a hole in the wall, which is used to hide Kenny's piggy bank away from those who wish to steal it (such as Freddie Fox). When closed, the panel is indistinguishable from the rest of the wall it is located on.
The wall panel is used to hide Kenny's piggy bank. He reveals it to his friend Paddy, while inadvertadely revealing it to Freddie as well. Kenny claims that Paddy would have never found out about the hiding spot if he hadn't shown it to him, which may be true though sadly is never confirmed. Later the location of the panel is put to Freddie's advantage when he both takes the piggy bank as well as using a fake foot to track mud away from the wall panel.