Secrets of the Inner Sea
Castle Falkenstein doesn't really have a skill that covers lying very well, so we're making a ruling.
For the sort of white lies told in social situations, that's Social Graces. However, the sort of lying that Dramatic Characters are likely to do, things like "We have no idea where that scientist went," that's covered by either Courage or Performance. As usual for overlapping skills, depending on the situation the GMs may choose one or the other, but all things being equal, you can use the highest one, unless one of them is Poor.