Castle ran his hand through his hair before rubbing at his exhausted eyes. Alexis and his mother had snuck in five minutes after Kate nodded off. He'd sent them away with Kate's apartment keys and a request for a couple of toothbrushes and changes of clothes for both of them. His mother gave him a knowing look when he said he'd be staying at the hospital overnight.
After the nurse moved them to a room, Kate did wake up long enough to reassure Lanie, Ryan and Esposito that she was going to be fine. Esposito warned her that Captain Gates had a mountain of paperwork for her to fill out for a job-related injury. Kate grimaced in mock pain and made a joke about the insurance paperwork being worse than being shot. Castle assumed from her lack of confusion at the name that Kate remembered who Gates was and probably why Montgomery wasn't in charge anymore.
She didn't let go of his hand the entire time her friends were in the room. Castle saw Lanie step on Esposito's foot when it looked like he was going to ask about it. Castle just tightened his grip and softly stroked the back of Kate's hand with his thumb. Eventually, Kate started yawning and everyone took their leave before she nodded off again a few minutes later.
Castle stole an unobserved moment to stroke her hair, thinking about his promise to himself to stop loving the woman holding his hand, and his unreasonably wise mother's belief that it wasn't possible to turn emotions off at will.