Mr. Mitt tells Annie there is an underwater passage in from the river that comes to the castle. The passage is big enough for a U-boat to enter and the pool is deep enough for it. Mr. Mitt tells Annie to stay upstairs, he is going down to surprise the sub crew. He tells her there may be shooting so stay upstairs. He goes down and Annie follows behind him. The sub crew surprise Mr. Mitt and hold him and his people at gun point. The sub crew goes to find the explosives. Annie is surprised when the man behind her said the package in the radio room must be the explosives.