Not Quite Duty-Free
Lucifer didn't stand alone in the airport. He wasn't worried about the two Demon's standing by his side, because only something non-human would recognise them; and he had incorporated his apparent wealth into the back-story of Morgan Campbell. Truth was money didn't matter as long as you were well-connected. And he was. If there wasn't already a Demon working in a certain industry, they didn't have to bypass the same rules as Angels when they claimed a new vessel, they just swooped in and sorted everything out. Something Lucifer was almost envious of, but he had made it that way, because essentially they were always Human, just a little... twisted.
He knew he would miss the game anyway. There was an art to it, slipping under the fence and exposing their weaknesses to manipulate them to your will. The stuff of beauty. He knew that he personally only found the challenges more worthy of his pursuit - case and point, Sam Winchester. All the more glorious would it be when that one word was uttered from the man's lips and he could slip into his skin. Once that happened, the stars would align and nothing could stop him. No one but Michael. Before all of that, he would pay Sam a visit. Not physically, because he still hadn't pinned down his location, even with all of his infinite resources - hence his employment of the Detective - but instead he would visit his mindspace. The only place he wouldn't be protected, while he slept. He could really wriggle in deep that way.
So yes, Lucifer stood in Heathrow airport by the check-in, he wasn't alone, not for the two Demons stood at either side of him - one tall and lean with a shock of black hair, the other slightly shorter and more rounded, but both looked equally menacing, with an air of power that seemed to radiate around them, almost sourced from Lucifer himself. The Archangel looked strikingly different standing there from when he first encountered John and Sherlock. He now wore a suit not dissimilar to the two men at either side of them, though his seemed to look more expensive. His hair had been tamed somewhat and he had used his own grace to - not repair - but tone down the appearance of the burns; physically they were still there but to the eyes of another, they were not so visible. He looked... presentable.
It was his intention completely to baffle the Detective and his Doctor, make them reconsider whatever conclusions they'd drawn, perhaps back-track them a little to buy him more time, and make them keener to focus on finding Sam rather than investigate him - which he had no doubt would happen soon if it hadn't already.
One of the men carried a small bag, which essentially held nothing. It was mostly a prop, but he supposed he could get away with it seeing as he was only supposed to be visiting England to meet them and try to get them to take his case - not that he had infact been summoned there by Sherlock Holmes' mortal enemy with the intent of aiding in killing both Sherlock and John. Something best kept between himself and Moriarty he supposed.
He was restless to begin the ceremony to bring and bind War to him, as he was to get in contact with Sam. Perhaps things he could do while he was supposed to be on the plane. His seat booked away from the others - so as long as they didn't keep too close of an eye, he could probably get away with this. He wasn't worry. But perhaps he should have been.