After Miranda disappears the second time, he calls Brock and drives out to his house in the country--a concrete bunker, now in shambles. Brock seems to be in shock, unable to say anything. Who was he and why did he call him?
Brock was one of Jeff's clients earlier in the movie. He was paranoid about terrorist attacks and overzealous with his equipment. When Jeff got him off the hook (apparently again) for attacking someone he mistook for a terrorist, he offered to let Jeff and one of his lawyer friends stay at his bunker in the event of an actual terrorist attack. So, I guess Jeff figured that Miranda would be safe there while he had to go work on that one case. Hence why Brock was so in shock after the destruction of his bunker. He was either caught off guard or surprised by their methods of attack (like the previous night at Jeff's, where they were using magic to open doors and stuff).
If you remember Tim Daly's character was Brock's lawyer in a case. Tim Daly's character remembered how fortified of a place that Brock had and that is why Miranda stayed there. When the new lawyer was actually one of the cult folowers and told where Miranda was at. That is why you saw the place in shambles because the cult came and got her.
Brock was a client of the law firm. He is all caught up in terrorism, and he has a bunker in the mountains that Jeff takes Miranda to, thinking she'd be safe there. Of course nothing is safe from black magic and spells, which the cult used to break in the bunker, leaving it in shambles. Miranda knew this, of course, and was just along for the ride to snare Jeff into his eventual human sacrifice. Jeff sees Brock totally in a catatonic state in what's left of the bunker, as a spell was put on him. This movie did NOT have a happy ending for anyone.