He released more air from his buoyancy, sank down to swipe the sand away, revealing a gap under the craggy reef. He shone his dive torch in – the kelp was hiding the entrance to a larger space.

A cave. This has got to be it.

There was no time for celebration. Now Forest was all business.

Time to see what treasures this cavern holds.

A clunking caught his attention. Sounds travelled better underwater, and Ahab had come down after him, trailing the rope attached to the buoy he’d left behind. The old man was tapping his dive computer against Forest’s oxygen tanks to get his attention. He showed a message written on his dive slate: WEAR YOUR BUOY!

Forest simply used his index and middle fingers to gesture to his eyes, then stabbed his finger at the cave, making the scuba signal of Look here.

Ahab floated down beside him, peering into the opening. He rubbed out the message on his slate and wrote: TOO DANGEROUS FOR YOU, HEAD TO BOAT.

They’d already had this conversation. Ahab had espoused the dangers of cave diving, explaining that a large percentage of diving fatalities was the result of people attempting to dive in caves without the proper training. That the way water moved in smaller spaces caused people to get stuck in crevices, that the walls scraped against equipment, that the lowered visibility set people into a panic, making them unable to orient themselves to the surface, a slow death by depleted oxygen tanks . . .

But Forest hadn’t made it this far by playing it safe.

Before Ahab could stop him, he was inside the opening.

Instantly the sounds of the ocean were softened, echoing, eerie. The kelp tickled him as he moved further.

If there was something in here valuable enough for Jesse to kill Alexandra . . .

The passage angled upwards, burrowing into the reef itself, and . . .

Stale air touched his face.

His torch lit up the inside of a cavern the size of a large room. He took his regulator out and took a breath.

Immediately his lungs tightened. He coughed, grabbing his throat, gasping, coughing again . . .

A second later Ahab had pushed Forest’s regulator back in. He held his own breather aside and whispered out the side of his mouth, ‘Breathe, Forest, the air is toxic in here . . .’

Eventually the terror eased and Forest was able to breathe deeply through his regulator again. He made to reach under his mask to wipe at the tears, but Ahab grabbed Forest’s wrist and shook his head, tapping the mask.

Mask stays on.

Forest had felt a lot safer under the water than in this cave with its dead air.