This is an extremely rare copy of Arrow of Death published by a company called Acorn Software Products, for the TRS-80. Not only is this the only Mysterious Adventure I have seen on disk, it is also dated 1982 while all other versions are 1983 or later. An earlier version of the first few games in this series exists, published in 1981 by Molimerx, which I have yet to locate. Acorn Software appears to be a company which published software exclusively for the TRS-80, however I can find no mention of this version of the game anywhere.