I remember reading this in elementary school sometime around 1984-1986. I think the story was part of a book of scary short stories, but for some reason this one stands out. The gist of the story is that some kid ends up in an abandoned house, realizes there is some sort of monster in there, and tries to get away. In the end, he somehow busts through a door/wall/window to escape, but the ending line is something about “And now the monster could get out too”.
It may have been that the kid and monster were in the walls of the house and there may have been ghosts of the monsters previous victim’s involved.
Vague enough for you?