Of course David would do that... he takes a lot of chances, doesn't he? Much like the Doctor.

Still, at least two of them know what's going on. Maybe, with the entity there, it could guide them back to the planet it came from and return it to a natural host. Hopefully...

Although, if this is still in the past, and the beginning was the present, I think it's going to be down to the wire. And now I think I know what they are going to try to do, and what that was all about.