Crowley stands between Hastur and Aziraphale, but he isn't certain that Hastur can see them. He must know they're there, otherwise why expose himself like this? Several reasons, Crowley's mind immediately supplies: #1) Hastur is not all that bright, and #2) Hastur hates Crowley. This is the opportunity to attack Crowley directly, and he will, with a vengeance, and whenever possible. He might not even be acting on orders, for all Crowley knows.

"There's a door in the back," Crowley says to Aziraphale. "Behind the toilets. I'll distract him, you turn and run."

He raises a hand up and a notecard appears, with the address of the temple on it, he thrusts it towards the angel.

"Meet me here."