The siblings had grown up in Hawaii, where they developed a passion for the sea. Their single mother fostered an early interest in marine biology and encouraged both children to learn to dive at a young age. Fraternal twins who were both athletic and adventurous, Dirk and Summer spent much of their youth on or near the water. Their interest continued into college, where both studied ocean sciences. They somehow ended on opposite coasts, Summer obtaining an advanced degree from Scripps Institute while Dirk garnered a graduate degree in marine engineering from New York Maritime College.

It was on their mother’s deathbed that they first learned the identity of their father, who ran the National Underwater and Marine Agency and shared the same name as Dirk. An emotional reunion led to a close relationship with the man they had never known. They now found themselves working under his tutelage in the special projects department of NUMA. It was a dream job, enabling them to travel the world together, studying the oceans and solving some of the never-ending mysteries of the deep.

Dirk kept the throttle down as they passed a fishing boat headed north, then pulled up a quarter mile later. As the boat approached the designated target, he killed the engines and drifted over the position. Summer walked to the stern and rigged her fishing line with an empty vial as a pair of Dall’s porpoises broke the surface nearby and eyed the boat with curiosity.

“Watch out for Flipper when you cast that thing,” Dirk said, walking onto the deck. “Beaning a porpoise brings bad karma.”

“How about beaning your brother?”

“Much, much worse.” He smiled as the marine mammals ducked under the surface. He scanned the surrounding waters, waiting for them to resurface, when he noticed the fishing boat again. She had gradually changed course and was now turning south. Dirk noted that it sailed on a circular course and would soon bear down on his own craft.

“You better make it quick, Summer. I don’t think this guy is watching where he’s going.”

Summer glanced at the approaching boat, then tossed the water vial over the side. The weighted apparatus quickly sank into the murk as a dozen feet of loose line was let out. When the line drew taut, Summer jerked it, causing the inverted vial to flip over and fill with subsurface water. Reeling in the line, she looked toward the fishing boat. It continued to turn in a lazy arc barely a hundred feet away, its bow easing toward the NUMA vessel.

Dirk had already returned to the wheelhouse and hit a button on the cowl. A honking blast erupted from a pair of trumpeted air horns mounted on the bow. The loud bellow echoed across the water but incited no reaction from the fishing boat. It continued to turn lazily toward a rendezvous with the research boat.