At the Tucks' house, what plan does the man in the yellow suit announce?

The man in the yellow suit announces that he will sell the water.

"It's very simple," said the man in the yellow suit. And, as he said this, the smoothness of his face began to loosen a little. A faint flush crept up his neck, and the pitch of his voice lifted, became a fraction higher. "Like all magnificent things, it's very simple. The wood—and the spring—belong to me now." He patted his breast
pocket. "I have a paper here, all signed and legal, to prove it. I'm going to sell the water, you see."
"You can't do that!" roared Tuck. "You got to be out of your mind!"
The man in the yellow suit frowned. "But I'm not going to sell it to just anybody," he protested. "Only to certain people, people who deserve it. And it will be very, very expensive. But who wouldn't give a fortune to live forever?"
"I wouldn't," said Tuck grimly.
"Exactly," said the man in the yellow suit. His eyes glowed. "Ignorant people like you should never have the opportunity. It should be kept for . . . certain others. And for me. However, since it's already too late to keep you out, you may as well join me in what I'm going to do. You can show me where the spring is and help me to advertise. We'll set up demonstrations. You know—things that would be fatal to anybody else, but won't affect you in the least. I'll pay for your assistance, of course. It won't take long for the word to spread. And then you can go your way. Well, what do you say?"