You hear something new from down the stairwell. Not just water burbling. There’s a slow, repetitive slap. You shine your torch down into the dark, and you can see nothing but the surface of the water. Which, incidentally, appears to have got closer. As your torch beam flicks around, you glimpse a pale hand holding onto the handrail.
For a moment, your heart leaps. You’re not alone. There’s someone else with you. Then it skips a beat, because you know you are alone, and there’s no one else with you. You press your back against the wall. What are you supposed to do? What does this night want from you?
The wet slapping of feet carries on. They seem to be in no hurry. Why would they? You’ve nowhere to go. Even if they take hours, you can’t escape. You’re surrounded by water. The rest of the world seems to have been swept away. It’s just this tower block, you and whoever it is coming up the stairs.
Would you rather know? Would you rather not know? You dither. Can you possibly evade them in some way? Lock yourself in a cupboard? You’ve lost your keys. Lock yourself in a toilet? The nearest ones are on the fifth floor. You’d have to go down, at the same time as … whatever … is on their way up.