She knows him too well. Everything about him tells Catherine that Nick is taking this personally. Again. As if it was his fault that the killer wasn't leaving them enough evidence to nail him.
"Hey," she says, touching his shoulder. She sees him realise that she knows, then he slumps against her.
"How do we do it, Cath?" he asks, her white knight become a lost little boy. "How do you... after Eddie?"
She smiles gently. "The way I always have, Nick, one day at a time. Some days are better than others. Any day with you in, for instance."