“Altana?”

“Like a little shack on the roof. A shaded place to sit, yes?”

“I should like to see for myself,” she said.

“Very well. If you insist. You will need strong legs.” He looked amused now as he watched her walk ahead of him. The second flight wasn’t quite so grand, and the third flight was a simple wooden stair going straight up. She reached the third-floor landing, trying not to let the man see she was breathing heavily. There were four doors, all shut.

He arrived beside her. “As you can see. No more staircase,” he said triumphantly. He opened one door to show a room shrouded in dust sheets. Then another, to an empty space, and then a third. Finally, he opened a door to what seemed to be a large broom cupboard or anteroom. It was stacked with old bits of broken furniture, planks, a stepladder.

“I am sorry, but someone has played a joke on you, I think.”

“Does the city of Venice waste its official stamps on jokes?” she asked. She insisted on walking into each of the rooms and had to admit that there was no staircase going up. Finally, she went into that big closet. It was dark inside, with a cobweb or two. She looked around, fighting off disappointment and frustration.

“I’m afraid you are right,” she said at last. “But I don’t understand . . .” As she examined the walls, she noticed what could have been the top of a door, behind a tabletop propped against the back wall. “Wait,” she said.

He was already heading away again. He turned back.

“I think there is a door at the back of this closet.” She moved a three-legged chair and then tried to shift the tabletop. “Help me move this,” she said.

“Please be careful,” he exclaimed. “It could be heavy, and we don’t want . . .”

But she was already dragging it aside until a doorknob was visible.

“There, look,” she said, pointing at it triumphantly.

He sprang forward to assist, and they moved the table aside.

“You see. There is a door.” She gave him a jubilant grin.

“Yes, to more storage, I expect.” He paused. “Oh no, un momento. It will probably be the way to the roof. To the altana mentioned in the plans.” He tried to open it. It didn’t move. “You see.” He looked up with the hint of satisfaction. “I’m afraid the door no longer opens.”

Caroline reached into her pocket and drew out the big key. “I wonder if this might help?” she said.

“What is this key?” he demanded. “Where did you get it?”

“My aunt left it to me.” Her heart beating rapidly, she put the key into the lock and turned it. After a moment of resistance, she heard a satisfying click. The door opened slowly, with an ominous creaking sound. Ahead of her a steep, narrow staircase rose into complete darkness.

“To the roof, you see,” the man said. “I don’t think you should go up. These old roof terraces are dangerous.”