While the Nightingale had a unique skill set, there were rare occasions where his abilities failed to be up for the task. When that happened, they would focus on more tactical applications, which were far more practical.
Risks were part of every job. More so in Lucien's type of work with no organization or guild backing him up. There was no way to pay off a fee if things got too hairy and if he got arrested? No way to buy the guards off either.
Operating this way was a risk in itself, but in turn, it allowed him far more anonymity and more specifically, his choice of not just targets, but payment as well.
One could even say that he worked this way because it was far more lucrative, but the reality was that he didn't want to be constrained by the rules of the thieves guild proper. It was far better for him to handle the situation in whatever way was proper for the moment. More specifically, he didn't have to worry about the consequences of his actions that would no doubt happen if he was constructed by proper rules.
In this case, Lucien was given only limited information about what he was to retrieve - an artifact of some kind. The question if it actually existed or not hadn't crossed his mind as he was used to operating on limited information. Defaulting on a contract was not an option and success via completion was ultimately the only situation that was possible.
Unless and only unless what he was after was a set up, for which would result in not just embarrassment, but pure rage. It hadn't happened as yet... though, even Lucien knew that it would occur eventually.
While he'd been watching for at least a week, he managed to grasp some information on a schedule. It may not have been the best documented, but it was something that Lucien could gain some assumptions from.
What he gained was enough that he could proceed as planned tonight.
There would be no more waiting or watching.
The Agent of Subterfuge would move in on his own terms - under the dead of night.
Entering was no doubt the easy part. Slipping in as a few had done the earlier. While a simple task on the surface, getting to the lower level was a bit more complicated as he didn't know what was down there, other than a general assumption.
So, as he went down the stairs, he was careful not to make too much noise. It was impossible at this point to know who was down there or exactly what he would face.
All that was known happened to be that it was quite possible the only reason he even was there in the first place was what he was contracted to obtain. It was supposed to be locked up tight in a back room, supposedly. That was, if this wasn't just a set-up.
It was why Lucien opened the door very carefully as he peeked inside the lower level. If there were one too many people around, he might have had to change tactics or something along the lines of out of what was the usual, but if it allowed him to get what was required? So be it.
Defaulting would only ruin his reputation.