Hermione threw a quick  Homenum Revelio when they entered the house, and when nothing was triggered, Dean and she separated and quickly scavenged for the plans. But then, in the middle of searching, the Death Eaters returned. And Hermione, cornered in a hallway with the plans clenched in her hands, froze, body stuck in fight-or-flight. Sweat clung to her skin in rivulets and she felt delirious in the heat. Enough so, that when she heard Malfoy speak out of nowhere, she almost thought she imagined him. 