doctor who - What was the purpose of the octagonal room in Heaven Sent?

There was an octagonal room, with an octagon in the centre of the floor. In the centre there was some sand and dust, with arrows pointing towards the central point.

What was the importance of that room?

Answer

The gap in the floor is a missing stone. It’s the tile that the Doctor digs up in the courtyard.

After he leaves the room with the octagonal gap, he goes into the courtyard and starts digging. When he first strikes the stone, we see his mind flash to the room with the arrows – it’s implying that this would fit into the gap. (We don’t see the full stone, but the Doctor can presumably feel the edges of it under the dirt, and feels the octagonal edges.)

This is the flashback image, which shows the space where the tile would fit:

It makes it clear that the message on this stone is important, and that this is part of the breadcrumb trail.

Why bury it at all? Two reasons:

• It forces the Doctor to dig a grave-like hole, the idea of which I’m sure amused the designer of the castle.


• The message isn’t too obvious, to try to throw him off the scent of the trap in Room 12.