"I don't know, but I don't think she has one," Benjamin said. "She is a patient who is allowed to help if I understood correctly, so I doubt they would have given her a key." He crossed his arms as he thought about it. "Shall we go for a walk? Maybe we can see someone who is careless with their key."
He had seen staff before, but he hadn't paid much attention to where they kept their card keys. 
"We can also prepare the best escape route while we're at it," he continued.