The Doctor guesses that the Daleks will destroy the planet as soon as he deactivates the force-field, but he realises that Rory's hideout is a telepad, via which they can teleport onto the Dalek Parliament ship.
The Daleks will destroy the planet as soon as he deactivates the force-field. This is what the Doctor guesses. Rory's hideout is a telepad. This is via which they can teleport onto the Dalek Parliament ship. He realises this.