S01E633: The Guardian of Time's Sword (2)

Conan deduces that Hoshina was stabbed with an umbrella, which fitted the description perfectly. A contraption on the mansion's clock tower set up by the culprit dragged the umbrella away and out of sight when it hit 6:00. The culprit is one of the party guests, Teigo Karube, who had designed this mansion and lost his clock technician friend four years ago. He reveals that the mistress treated the clock technician like trash and even threw away his friend's beloved clock, so he killed her in order to avenge his friend.