They have no reason to believe that the Bell and Book is a pub favored by Death Eaters, but even so, they arrive a few at a time. It’s a busy floo connection, and they’re unlikely to arouse suspicions, but Tonks plans meticulously. She wants Draco and Hermione with her so that, as soon as they spot the expected boats, they’ll be in the best position to eavesdrop. The sun doesn’t set until eight, and the dusk will linger, so they won’t take up their positions until nine o’clock. The plan is to flank the French Death Eaters, subdue them, and apparate them to a disillusioned safe house in the High Weald for interrogation. They’re expecting approximately twenty, so they’ll be outnumbered, but they have the element of surprise.