Episode 396: Big Adventure in the Eccentric Mansion - The Resolution
Scenario: The old lady nearly gets chopped up by four swinging blades when she steps on a trap. Conan realizes that if one stands in the right spot the blades will not harm you and that one of the blades actually has a handle allowing him to swing over towards the sword. The sword contains the last clue, which leads everyone back to the pond. Mitsuhiko accidentally discovers that the diamond is at the bottom of the pond. The first treasure hunter dives in after it while the second pulls a gun planning to kill everyone and take the diamond for herself. Conan is able to tranquilizer her, but when the treasure hunter comes back up with the diamond the spring starts to pour into the pond causing a massive flood. The only way to stop the flood is to put the diamond back. The old lady turns out to be Kaitou Kid who knew all along that the diamond was unable to be stolen, and Conan allows him to escape on his hang-glider.