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human
[Skyrim] What was the Thalmor plan at Helgen?

When the Dragonborn finds the Thalmor dossier on Ulfric Stormcloak at the embassy, it includes a passage that says "As long as the civil war proceeds in its current indecisive fashion, we should remain hands-off. The incident at Helgen is an example where an exception had to be made - obviously Ulfric's death would have dramatically increased the chance of an Imperial victory and thus harmed our overall position in Skyrim." 
To me, this text, combined with the fact that there were Thalmor in Helgen when the DB's carriage arrived, suggests that the Thalmor had some plan in place to break Ulfric out of Imperial custody that was made irrelevant by Alduin's attack. What was their plan?
gpt
The Dominion has technical custody of all 'Talos worshipers' under the inquisitorial implementation of the White-Gold Concordant. As such, Ulfric, the titular head of the movement, is rightly under THEIR jurisdiction. 

Consider Helgen's location. We know Ulfric and his compatriots were captured around Darkwater crossing, and that Tullius is based out of Solitude. Regardless of where they were going, they would have to pass through Whiterun Hold, so there's no reason to state that their southward location was to avoid Balgruf's neutral territory. Instead, it's rather clear that Tullius was not heading to Solitude as you would expect. 

So what's south? The pass to Cyrodiil for one. It seems likely that Tullius was attempting to get Ulfric to the Imperial City for whatever fate awaited him there. This was almost certainly an attempt to avoid the Thalmor Inquisition, based out of the Embassy near Solitude, altogether. Meaning, Tullius was already disobeying the Thalmor authority by trying to smuggle a prisoner out of the province...

But the Thalmor found out, and when Tullius caught wind of their approach, he opted for summary execution rather than turning Ulfric and his men over to the Dominion. Whether he suspected Elenwin's agenda or was simply trying to offer Ulfric a more honourable death, we can't be certain, but it's clear at least to me that the lack of Dominion presence during, or following the executions is proof that they were shown the door after Tullius refused to turn Ulfric over.

Now, why was Elenwin there? Easy. Ulfric was, again, rightly under their jurisdiction. Had Tullius followed his mandate to the letter, all Talos worshippers should have been handed over to HER custody. She would then ensure that Ulfric and his men 'escaped', likely with everyone but Ulfric being killed, thus allowing the Civil War to continue. She probably didn't expect Tullius to have the balls to turn her away though.