Cas understood that sadness. He didn't argue with Peter and, as it turned out, he didn't need to. He shifted a little close to his friend, letting his hand brush Peter's arm. "I... I know a way in," Cas confided. "It won't be easy but I have help. It can be done." In theory.
It would be tough and dangerous but so was Hell and he'd do that again in a heartbeat for less that he was fighting for in the Cage.
"We will get them back, Peter," Cas said again. "As soon as we can." Castiel felt flashes of bravado every time he had to assure someone, and convince himself. It helped to keep him going. If he said it enough...
He had little to say about it most of the time and nothing to say on anything else. No food, no television, no games, no distractions. Only these small moments aside. He held Peter's gaze. "I can do this."