Sneak around, snap some necks, plant some C4, do whatever it takes to survive and complete an assigned mission. 22 missions in total. If you have trouble with a level, go into the menu and look at hints.

Arrow keys to move around. 'R' to restart the game. 'M' to access menu.
'Z' to place C4 explosives. 'X' to detonate the C4.
Spacebar to - snap neck; tap on wall (while on wall); and use object.