Here’s what you’ll learn when you read this story:

• Derek Batten, Peter Tunstead, and James Tunstead set sail from Airlie Beach in Queensland, Australia, with a plan to sail around the continent’s northern coast on Batten’s boat, the Kaz II.
• Just a few days after they embarked on their trip, their boat was spotted adrift far off from their first stopping point on the coast.
• When authorities tracked down and boarded the ship, the cabin was tidy, with food on the table. But the three men were nowhere to be found.

On the morning of April 15, 2007, around 8 a.m., Derek Batten steered his boat, the Kaz II, out of Airlie Beach’s Abel Point Marina and into the waters along the northeast coast of Queensland, Australia. Joining the 56-year-old Batten aboard the catamaran were his next-door neighbor, 69-year-old Peter Tunstead, and Tunstead’s 63-year-old brother, James Tunstead. The three—who were by no means expert sailors, but had some experience under their belts—were en route to Townsville, their first stop on a long sailing trip that would see them navigate the northern coast of the continent and then travel down to western Australia (where they lived), just south of Perth.

They’d brought a camera along to document their adventure, and even in the first few hours of their trip, they’d been using it frequently. In footage shot around 10 a.m., James trained the lens on their skipper, Batten, who was manning the helm, armed with a blue coffee mug. Both the mainsail and headsail were let out on opposing sides of the boat. James panned the camera to the back of the 40-foot catamaran and captured video of Peter sitting on the aft stairway, beaming up at his younger brother from under a floppy hat and sunglasses, with a line cast out to choppy waters from the fishing rod in his hand.

For the moment, everything seemed alright. After dutiful planning and mapping, the trip of a lifetime had gotten off to a pleasant start, and weeks of adventure lay ahead of the trio as they sailed back home to Perth.

But they would never make it home. From behind the camera at 10:05 a.m. that morning, James unknowingly captured the last moments that anyone else would ever see of the three men’s lives. A short (but still unknown) amount of time later, Derek Batten, Peter Tunstead, and James Tunstead vanished completely.

Around 3:45 p.m. on April 18, a Coastwatch surveillance helicopter noticed the Kaz II drifting about 80 nautical miles off the coast of Townsville. Its mainsail had been damaged and there was a massive tear in the middle of the headsail, but despite that, the ship seemed to be moving fine. The helicopter still radioed the sighting into the authorities on the coast, who hadn’t received any distress calls, and Townsville Water Police senior constable Jason Jesse attempted to contact and identify the ship, to no avail.

After the night had passed and no response from the boat had come in, despite numerous attempts at contact, Jesse asked Coastwatch to search for the vessel again. Once again, a Coastwatch helicopter located the ship, but this time, the Kaz II was sitting “dead in the water.” A rescue team sprang into action.

It wasn’t until April 20 that rescuers were able to reach the Kaz II, at which time a surreal scene greeted them. “The engine was running, the computers were running, there was a laptop set up on the table which was running, the radio was working... and there was food and utensils set on the table ready to eat,” said Jon Hall, a spokesman for Queensland’s Emergency Management office, according to a BBC News report—but the boat’s crew had vanished.

Peter Tunstead’s fishing rod was tethered to a stanchion, and the fishing lure was wrapped around the portside rudder. The boat’s radio and GPS were fully functional, and there were no life jackets missing. In fact, aside from the damaged sails, there was almost nothing abnormal about the state of the Kaz II—except, of course, for the complete disappearance of the three men who were on board when it set sail.

Around the time when the boat was found, a search was getting underway. The endeavor rallied Volunteer Rescue Units from several nearby towns, the Townsville coast guard, two rescue helicopters, nine airplanes, and two commercial vessels. But despite covering surrounding towns and the water near where the boat was found, there was no sign of the men, and the search was called off at 4 p.m. on April 21. Another brief search was attempted a couple of days later, but it was similarly fruitless, and it didn’t last long.

After authorities found and searched the catamaran at sea, the boat was towed to shore, at which point crime scene investigators scoured the boat for evidence of foul play or a third party’s involvement. But after thorough observation of the Kaz II, the investigators found nothing suggesting a struggle.

There was some helpful evidence still on board the boat, including the camera (from which the last footage of the men was recovered) and the GPS. Data from the boat’s GPS indicated that shortly after the crew took off from Airlie Beach, it headed northeast from its route towards an area that was experiencing some squalls, but the general tidiness of the ship indicated that the Kaz II wasn’t thrashed about in any way. GPS data from later in the afternoon of April 15 showed that the ship was adrift.

Over a year later, starting on Aug. 4, 2008, an inquest led by Queensland state coroner Michael Barnes heard 27 witnesses testify to help authorities piece together the timeline of the “ghost ship,” as it was being called. Barnes and his team were hoping to find some missing piece of the puzzle that had eluded the investigation thus far—some explanation of what happened on that boat beyond the reasonable declaration that the three men were now dead. But among the other sailors who had seen the Kaz II from far off, various family members of Batten and the Tunsteads, and the investigating authorities, there was no eureka moment to be found.

“I can not be so definitive about the circumstances under which the deaths occurred,” Barnes wrote in his official report from the inquest. Based on the available video, eyewitness accounts, and the evidence left on the boat, he deduced that what unfolded shortly after James Tunstead turned the camera off was a bizarre, unfortunate, and ultimately fatal scene.

Because the fishing lure was found wrapped up in the rudder, Barnes believes that one of the Tunstead brothers fell into the water while trying to untangle it, and the other Tunstead then jumped in to rescue him. As was revealed in the inquest, a worker at the marina from which the trio set sail gave them a ride to the yacht, and on the way, the three joked about Peter Tunstead’s limited swimming ability. If he had fallen in, James would certainly have attempted to help his brother—and authorities found James’ t-shirt and sunglasses on a chair on the rear deck of the boat. They weren’t there in the video.

With the Tunsteads overboard, what happened to Batten is slightly less clear. For the skipper to have turned the boat around to rescue the brothers (the rear platform on the boat, which was right on the waterline, would have been extremely difficult for the brothers to hoist themselves onto), he would have needed to let the sails down and run the motor. According to Barnes, any deviation in the boat’s direction or wind speed would have swung the sail across the deck if it wasn’t deliberately controlled by Batten. The blue coffee mug that was seen at the helm with Batten in the video was found near the boat’s life ring when authorities reached the boat. If Batten had gone to throw the life ring to his friends, the sail could have swung across the deck and easily knocked Batten overboard.

“Once the three men were in the water, there was very little chance they could get back on the boat as it was blown before a 15-knot wind and they struggled in lumpy seas,” Barnes wrote in his report. “It would be beyond their reach in seconds[…]. From that point, the end would have been swift.”

Unsurprisingly, Barnes’ conclusion was met with a number of other theories. Many think that the three men were simply knocked overboard by rough seas—but that wouldn’t explain the tidy state in which the Kaz II was found.

Hope Himing, Batten’s niece, was adamant in a BBC report that the results of the investigation didn’t add up. “The fenders (an air-filled device meant to absorb contact from another boat) were out on their yacht, and the only reason you ever put them out is when another boat comes aside or if you come to rest against a wharf,” she said, proposing that the three may have left their vessel for another boat, forcibly or otherwise. However, an expert noted that smaller boats like the Kaz II commonly leave their fenders out at all times. Indeed, the fenders were also visibly deployed on the video, and eyewitnesses to the boat’s departure also said they were already hung over the side of the boat.

Every possible theory—from Barnes’ thorough reasoning to the unlikely-seeming role of rough seas—will always run up against the frustrating acknowledgement that whatever actually happened on that boat will probably remain a mystery for good. The only certainty is that Batten and the Tunsteads were never seen again, leaving behind few answers and nearly infinite questions.

“You think you’ve worked it out and then something doesn’t fit,” Keryn Grey, daughter of James Tunstead, told the Sydney Morning Herald. “Nobody knows. Our thoughts just keep going round in circles.”