SPOILERS:
Hermione apparates with Harry to the Forest of Dean to set up camp at a new location. Harry, keeping watch late at night, sees and follows a Patronus in the form of a silver doe to a frozen lake in which the Sword of Gryffindor lies.
In his attempt to return to the surface after he dives into the freezing water to retrieve the sword, Harry is nearly strangled by the locket around his neck as the lake freezes up over him.
He is saved from drowning by Ron, who reveals he was shown the way back to his friends by the Deluminator. Harry and Ron both agree to destroy the Horcrux now that they have the sword. Harry commands the Horcrux to open using Parseltongue, and Ron slashes the Locket with the blade.
They return to camp together. Ron expected to be welcomed back graciously but was in for a shock when Hermione started punching him furiously instead. Harry had to be the mediator between them.