Two teams descended into Norway’s Plura River, and two men did not come out. Now their surviving friends are faced with a secret mission to recover the bodies from a cave more than 100 meters below.

"You just cannot practice facing a dead friend at 110 meters."

That simple statement sums up the drama and tension of Diving Into the Unknown, a new cave-diving adventure documentary by director Juan Reina that tells a gripping tale of friendship, commitment and coping with loss. It’s set for worldwide iTunes release April 3, with DVD releases to follow in May.

“What are you willing to sacrifice to bring your friends home?” That’s the question posed by the film’s tagline, and it’s at the heart of the 85-minute documentary, shot in Finnish, English, Swedish, Norwegian with English subtitles.

In 2014, two teams of Finnish divers entered a cave in Norway’s Plura River at separate points, looking to meet in the middle, but a blocked passage and a moment of panic claim two lives. When the official recovery operation was called off by Norwegian and British authorities after being deemed too risky, the survivors set out on a secret mission to retrieve the bodies themselves.

Diving Into the Unknown made the rounds last year of the film-festival circuit, including a good reception at festivals in New York, Munich, Helsinki, Edinburgh and New Zealand. The Hollywood Reporter gave Diving Into The Unknown a thumbs up in November, likening it to the 2011 cave-diving thriller Sanctum, but praising its focus on the psychological challenge: “Not only are the men attempting to do something they've already failed at (in secret this time), they understand that what awaits them is a challenge far greater than they've encountered on normal outings.”

Reina uses maps, self-filmed material and after-the-fact interviews to supplement “astounding” GoPro photography.

“The practicality and determination those left alive demonstrate is incredibly uplifting,” wrote a reviewer for the Edinburgh International Film Festival. “Where Reina's film really elevates itself is in an efficient inspection of the psychological devastation of this ordeal.”

Says one of the divers, “I do everything I can not to die while diving.” Words to live by.

Learn more at divingintotheunknown.com.

Download film from iTunes.