Shagrat was the captain of the Orc garrison in the Tower of Cirith Ungol, the fortress that guarded the high pass into Mordor above Minas Morgul.1,2
On the night Shelob stung Frodo, Shagrat's Orcs came down from the tower and met a company from Minas Morgul under Gorbag. Sam, wearing the Ring and following unseen, overheard the two captains talk. From them he learned that Frodo was not dead but only stunned by Shelob's poison; that any spy taken was to be held unharmed, with his gear sent to Lugbúrz, the Dark Tower; and that both captains were weary of their masters and talked of slipping away somewhere with a few trusty lads.1
Frodo's mithril-coat set the two garrisons quarrelling over the plunder, and they fought through the tower until almost all of them were dead. That is why Sam found it nearly empty when he came to rescue Frodo. Shagrat survived, killed Gorbag, and fled towards Barad-dûr with a bundle of Frodo's belongings.2
Interpretation At the Black Gate the Mouth of Sauron showed Gandalf Frodo's mithril-coat, an Elven cloak and Sam's short sword. The text does not say how they reached him, but Shagrat's bundle, bound for the Dark Tower under orders, is the obvious road.3,2
Sources
Citations name the chapter rather than the page, so they work in any edition. The colour of each note shows what kind of source it is.
- Published story The Hobbit and The Lord of the Rings as Tolkien published them.
- Published story The Two Towers, Book IV, ch. 10, “The Choices of Master Samwise”
- Published story The Return of the King, Book VI, ch. 1, “The Tower of Cirith Ungol”
- Published story The Return of the King, Book V, ch. 10, “The Black Gate Opens”