The Trap is a short story by H.P. Lovecraft and Henry S. Whitehead. It was first published in Strange Tales, March 1932.
Synopsis[]
A schoolboy becomes trapped inside a mirror connected to the Fourth Dimension. The mirror world he is sucked into contains people from different past centuries as it is actually the creation of the Luciferian wizard Axel Holm who created it to try and gain immortality.
Behind the Mythos[]
The boy who passes through into the mirror realm and is eventually returned to Earth is discovered to have had his internal organs and handedness swapped. In other words the bilateral asymmetry of his body was physically changed to that of his "mirror image".
The reference to the Fourth Dimension in this story is allied to Hyperspace and other dimensions used in the Mythos as means of travel or moving from the third dimensional reality with which we are familiar.
A world within a mirror is also of particular relevance as being the Lovecraftian equivalent of Wonderland. Yet another Mirror Dimension is part of the Evil Dead setting.