After Sam, Frodo and Gollum/Smeagol continue on their way to Mordor, the resurfaced Gollum leads them into the lair of Shelob - an ancient spider-like monster - where Frodo is "killed." Sam takes Sting and becomes the new Ringbearer (albeit for a while) and leaves Frodo's body in Shelob's lair. A little while latter Sam hears a band of Mordor Orcs talking (he slipped on the Ring to not be seen and found that his hearing was heightened with iton) about a victim of Shelob's that they found and how he was left for dead. It turns out Shelob's poison doesn't kill but leaves in a state very much like death so she can dine on her victims at her leisure. Sam realizes who they are talking about is Frodo and he sets out to rescue him.

TTT had ended in a very dramatic fashion with Sam marching of with Sting and the Ring after Frodo had "died" and then reveal him to actually be alive 30 to 40 minutes into ROTK.

Peter Jackson said he had several unsuccessful tries at included a truncatedversion of the Scouring of the Shire as this is the point in the story when Saruman's life comes to an end but was unable to pull it off without the film running for one extra hour. This is why Christopher Lee has been reported to have filmed his character's death sever times in sever different ways. I guess they may just have Wormtongue slice his throat in the scene where Mithrandir visits Curin at Orthanc and and Pippin first gets a holdof the Palantir.