In A New Hope, why does Vader think they must be trying to return the stolen plans?

Question

I've been watching Star Wars for years, and I just caught these lines:

INT. DEATH STAR - CONFERENCE ROOM

Tarkin pushes a button and responds to the intercom buzz.

TARKIN
Yes.

VOICE (over intercom)
We've captured a freighter entering the remains of the Alderaan system. It's markings match those of a ship that blasted its way out of Mos Eisley.

VADER
They must be trying to return the stolen plans to the princess. She may yet be of some use to us.

What? Why would someone with the only copy of the stolen plans take them back to the Death Star, to give them to the princess, who is in detention there? He didn't say they may be trying to rescue her, or that they were probably destined for Alderaan.

The question is not about Luke/Obi-Wan's motivations, or why Vader let them 'escape' later. My specific question is:

Why does Vader assume 'they' must be trying to return the plans to the princess?

Anyone who has now come in possession of the plans must know the princess was captured, that's why/how that person now has the plans.

Answer 1

Vader doesn't know that the Rebels know that she's been captured, all he knows is that the plans were probably in the memory of a droid and he certainly doesn't know that Leia was able to record a message describing her capture.

He assumes that she shoved it into an escape pod and sent it to her Rebel contacts on the surface and he assumes that the Rebels are trying to return the plans to her at her likely location; Alderaan. Note that with no plans on board, her diplomatic credentials should have been enough to get her out of trouble.

When the same ship that was reported "blasting its way out of Mos Eisley" turns up in the Alderaan sector a few hours later, Vader correctly surmises that it's a Rebel craft and decides to use this ("She may yet be of some use to us") as an opportunity to ensnare the Rebel High Command. He cleverly tricks the Princess into escaping on a ship (having fitted it with a homing beacon) knowing that she'll head straight to the Rebel's secret base of operations.

Answer 2

I think you answered your own question. They were heading to Alderaan to hand the plans over to the head of the Alderaan government and center of the opposition to the Empire. They didn't know that Alderaan had been destroyed until they got to where it used to be (although Obi Wan knew something had happened, he didn't know what).

They certainly weren't expecting to run into the Death Star, or they wouldn't have mistaken it for a small moon. And they didn't know that Leia had been imprisoned on the Death Star until R2-D2 discovered it while plugged into the Death Star's computer system. I distinctly remember, after they were on the Death Star they had R2 plug into the DS's computer system to find out how to disable the tractor beam. After Obi Wan left to take care of that, R2 started getting excited. According to C-3PO he was saying something to the effect of "I found her! She's here!". Then C-3PO says something like, "Oh. Dear! She's scheduled for termination!"

Unless Lucas has retconned that part, too, they had no idea Leia was in the neighborhood until they were on the Death Star.

Answer 3

The best and simplest answer is that he did figure they were bound for Alderaan, so that it might have made a little more sense for Darth Vader to have said "the princess's allies" or "Alderaan," instead of "the princess," but that he roughly means "the princess (if they haven't heard from the senate that all on board her ship are dead), or, you know, her dad or other scummy, rebel-sympathizing buddies, on Alderaan, which is totally her home to which she presumably meant to return." I don't think Vader thinks anyone is purposely delivering the plans to someone in a jail cell in the middle of the Empire's fearsome fortress, nor does he have any reason to believe anyone knows the princess is even there.

Dramatically, in terms of the screenwriting choice, it might be argued that personalizing it this way highlights and enhances the personal, emotional connection the audience feels to our heroine Leia, and between her and our plucky heroes.

Furthermore, regarding the comment that anyone with the plans would know the princess was in the hands of the Empire, I don't think so and it would have been an unjustified assumption for Vader to make. They might think she was dead--if the Empire's message to the Senate had been delivered and distributed already. Otherwise it's at least as likely they'd expect her to return to Alderaan soon enough, as intercepting her ship and holding her prisoner was an unexpectedly "bold" and "dangerous" gambit on the part of the Sith Lord, considering her diplomatic status and relationship to the government:

COMMANDER Holding her is dangerous. If word of this gets out, it could generate sympathy for the Rebellion in the Senate.

Answer 4

TL;DR Luke, Han and Obi Wan do not know about the destruction of Alderaan when they set out. It's not until they arrive that they find it is gone.

They were trying to return the plans to Alderaan, not to Leia. They did not know that the planet was gone.

Vader was simply stating what their likely plan was based upon the fact that they did not know these about Alderaan being destroyed. Vader said they were trying to return the plans to Leia because he was assuming they did not know she was captured.

Answer 5

Princess Leia gives specific instructions in her plea:

I regret that I am unable to present my father's request to you in person, but my ship has fallen under attack and I'm afraid my mission to bring you to Alderaan has failed. I have placed information vital to the survival of the Rebellion into the memory systems of this R2 unit. My father will know how to retrieve it. You must see this droid safely delivered to him on Alderaan.

So two things:

1. She was going to Tatooine to get Obi-Wan. This makes sense, the Death Star is a critical threat to the Rebellion, getting one of the last known Jedi in existence makes perfect sense.

2. Knowing she is about to be captured, she sends the droids to Obi-Wan, trusting that he will get the plans to her father. Bail is a founding member of the Rebellion and would be the obvious choice to start mounting the counter-offensive.

Remember, at this point the idea that the Empire would use the Death Star on an Core World is laughable. The Rebellion is worried about their bases and ships being targeted and they've taken extreme measures to put their bases only on uninhabited worlds (Yavin, Dantooine, and later Hoth) to prevent reprisals. Everyone is shocked when Tarkin uses it on Alderaan, and this happened while the Falcon was in hyperspace, there was no way for them to find out what happened ahead of time.