This is my idea of what might have happened in that dining room on Bespin. Please be kind; it's my first attempt at Star Wars fanfic!
Disclaimer: George Lucas owns everything, of course.
The pair entered the stark white room – its pristine décor marred only by Vader's dark countenance and the mottled armor of Boba Fett – with their hands clasped together. Chewbacca followed Han's lead, though it was likely the Wookiee would have much rather begun by tearing the stormtroopers apart, and finishing up with Lando. As the doors slid smoothly shut, the trio looked more closely at the room, the shock of Vader's presence fading to allow their suspicion and fear to grow.
The table was set, and the food arranged elegantly. Leia realized grimly that Vader wasn't able to eat through his mask, so the meal was solely prepared for them. Well, she knew better than to put anything arranged by Vader into her mouth. Her lips set into a scowl so vicious it would have stopped even persistent Han from picking a fight with her, as he so often had in their days of bickering. Those days seemed remote as the very same Han Solo pulled out a chair for Leia, temporarily releasing her hand to push her closer to the table, then seating himself directly to her left, separating her from Vader.
Despite her terror, Leia's heart swelled with affection for the rough-edged smuggler – her smuggler – who never failed to try to protect her, even if he was usually only marginally successful. With Boba Fett hovering behind Vader's chair, it was obvious that Han's run from Jabba the Hutt was over, and Leia could not bear to think of what might happen next. All the worries she had harbored since Ord Mantell painfully surfaced again, nearly bringing tears to her eyes, though she tried to compose herself; no need to give Vader any satisfaction by crying.
She reached over and snatched Han's hand back in hers, eliciting a glance from him. His eyes showed a flicker of concern before he turned back toward Vader, his face set once again into a blankness honed during many games of Sabacc. "So, Lord Vader," he drawled, "Are we entitled to know why you've called this little dinner party?"
Vader answered simply, "I would advise that you and your companions eat now; I can guarantee it will be your last meal for quite some time."
"Not one for small talk, eh?" Han replied sarcastically, but a squeeze from Leia's hand prevented him from saying anything more. She had been avoiding looking in the direction of the Sith lord, as his presence left her nearly paralyzed by her memories of her time on the Death Star. Though she was in fact hungry, and was sure that Han and Chewie felt the same, none of them made any move to eat. The room was heavy with silence rhythmically punctuated by the metallic wheeze of Vader's breathing apparatus, and no one even stirred for several minutes.
Finally, Vader stood up from his chair at the head of the table. Before leaving, he turned to Lando and ordered, "Take the Princess and the Wookiee to the holding cells. Captain Solo will be brought to me." Boba Fett trailed along in Vader's wake, ever the dutiful bounty hunter.
Lando reached for Leia's arm to lead her out as well, but she jerked away and hissed, "Give me a moment!" She gently brushed a stray lock of Han's hair back and cupped his face in her small hands, her gaze locked with his.
"Sweetheart…" he murmured, and then was glad to find Leia's lips on his own, saving him from finding words to express what he was feeling. They leaned forward and deepened the kiss, both as desperate to offer comfort as they were to receive it.
Lando reluctantly cleared his throat. He knew that from there on out, Han and Leia would have no reprieve; how could he begrudge them this moment? But at the same time, the threat of displeasing Vader and bringing further strife to Cloud City forced him to motion the stormtroopers to grasp Han by the shoulders and pull the two apart.
At their sudden separation, Leia felt a chill race up her spine and a flash of a feeling of grave foreboding. Han saw the split second of sheer terror in her eyes and lunged just far enough from the stormtroopers' grip to press a kiss to her forehead before being yanked back once more.
As Han was pushed out of the room, he stole one last backward glance at Leia, and then disappeared around a corner. And for the first time in years for reasons other than the loss of Alderaan and her father, a tear rolled down the Princess' cheek.