DIRECT.DAT
A single 9 byte/null terminated string, that is the path to the save slot the battlescape game was loaded from.
This file is only used if indicated by the SAVEINFO.DAT file in the missdat folder. Otherwise, the battle is a new one, and a new tactical map is generated from the seeder files also in the missdat folder.
(Note to self - since the map isn't saved to the harddrive unless a savegame is made, how is terrain stock collection stored at the end of battle? Alloys, Alien Navigation, etc...)