“I haven’t. He’s not my father, that man. He’s only my guardian, but he makes me call him father whenever we’re on a job together.”

“A job? What sort of job?” said Julian.

“Oh any kind — all beastly,” said Martin. “Snooping round and finding things out about people, and then getting money from them if we promise to say nothing — and receiving stolen goods and selling them — and helping people like the men who are after your uncle’s secret…”

“Oho!” said Dick at once. “Now we’re coming to it. I thought you and Mr Curton were both suspiciously interested in Kirrin Island. What’s this present job, then?”

“My guardian will half-kill me for telling all this,” said Martin. “But, you see, they’re planning to blow up the island — and it’s about the worst thing I’ve ever been mixed up in — and I know your uncle is there — and perhaps George too now, you say. I can’t go on with it!”

A few more tears ran down his cheeks. It was awful to see a boy crying like that, and the three felt sorry for Martin now. They were also full of horror when they heard him say that the island was to be blown up!

“How do you know this?” asked Julian.

“Well, Mr Curton’s got a wireless receiver and transmitter as you know,” explained Martin, “and so have the fellows on the island — the ones who are after your uncle’s secret — so they can easily keep in touch with one another. They mean to get the secret if they can — if not they are going to blow the whole place sky-high so that nobody can get the secret. But they can’t get away by boat because they don’t know the way through those rocks…”

“Well, how will they get away then?” demanded Julian.

“We feel sure this hole that Timmy found the other day, leads down to the sea, and under the sea-bed to Kirrin Island,” said Martin. “Yes, I know it sounds too mad to be true — but Mr Curton’s got an old map which clearly shows there was once a passage under the sea-bed. If there is — well, the fellows across on the island can escape down it, after making all preparations for the island to be blown up. See?”

“Yes,” said Julian, taking a long breath. “I do see. I see it all very clearly now. I see something else too! Timmy has found his way from the island, using that same passage you have just told us about — and that’s why he’s led us back here — to take us to the island and rescue Uncle Quentin and George.”

There was a deep silence. Martin stared at the ground. Dick and Julian thought hard. Anne sobbed a little. It all seemed quite unbelievable to her. Then Julian put his hand on Martin’s arm.

“Martin! You did right to tell us. We may be able to prevent something dreadful. But you must help. We may need those spades of yours — and I expect you’ve got torches too. We haven’t. We don’t want to waste time going back and getting them — so will you come with us and help us? Will you lend us those spades and torches?”