Mephista's first thought upon reaching the castle is, Where is everybody?
At any time of day, the courtyard of the castle is usually alive and buzzing with people—courtiers lounging by the fountains, petitioners awaiting their audience with the throne, sometimes even musicians playing lively music. The place is all but empty, now.
When Mephista travels anywhere—always dressed in the finest of clothes, of course—he's usually trailed by at least a half dozen people, most of them the secretaries and various adjuncts it takes to keep the gears of his merchant house well-oiled and functioning. Not today, though. This morning he received an official summons with the king's own seal on it, but signed with a name he doesn't recognize. He was a little irritated by it, actually. One thing that's kept him in business so long is his extensive information network. He's got little birds everywhere, little birds who sing beautiful songs to him so long as he give them what they want. But this summons he knew nothing about. He doesn't like being surprised.
From one of the sentries he learns of the audience the king is holding in the Great Hall, but that doesn't interest him. He prefers to keep his physical person separate from politics and allow his little birds to keep him informed of the political currents in the kingdoms. So while the court busies itself in the Great Hall, Mephista goes in search of something to pass the time until the king is ready to see him.
At first he simply wanders the halls, nodding and smiling at the people he knows as they pass for he frequents the castle often on business and many of the courtiers know him personally. His blood hasn't a drop of noblility in it, but he's got more money and more assets that half the court put together and that's enough earn him a place here. And it's not an infrequent occurrence for him to offer friendly loans to those of the nobility who fall on hard times and wish to maintain their standard of living—at a reasonable interest rate of course.
Eventually, he inquires from a page the location of Tarlaka's rooms and heads in that direction. Captain Tarlaka, he reminds himself. She's probably in the Great Hall, but it couldn't hurt to stop by her rooms just to check. When he reaches the door, he knocks but doesn't bother to wait, instead opening the door and poking his head inside. "Helloooo? Tarlaka? You here, love?"