Their first attempt ends tragically as the mine detonates during retrieval, destroying the pontoon and revealing a hydrometer mechanism triggering the blast.

The team then successfully disables a second mine underwater, but onshore, as the group leader Ivanov dismantles it, a relay activates, causing an explosion and killing him.

Lieutenant Ukhov proposes bombarding the channel with depth charges, discovering that paired bombs prompt detonation.

The only remaining team member, inexperienced graduate student Makarin, undergoes accelerated diving training and raises the mine himself.

Severely injured yet alive, Makarin realizes he has found a way to neutralize the mines, ensuring the fleet’s pathway remains open.