You are flying a small drone through a collapsed five-storey building, looking for survivors. You see the world in 3D through the drone's own light, so only what is close to you is lit — everything beyond a few metres is darkness.
How to find someone. A survivor within range shows as a green dot. A solid pulsing dot is on your floor — fly onto it and it counts automatically. A dashed hollow ring labelled ▲ 1 floor or ▼ 2 floors is not on your floor, and flying over it will do nothing at all until you change floors.
How to change floors — one key. Tap SPACE (or the round blue button on a phone). One tap moves you a whole floor; there is nothing to hold. It only works where there is a hole, so when a survivor is on another floor every cell you could pass through starts pulsing blue — fly onto one and tap. The button only appears when the move is actually available, and the column on the right shows all five floors, which one you are on, and how many people are still waiting on each.
Then get out. Once all three are found, fly back to the dashed blue square you started at before the battery runs down.