How should I handle this work dilemma?

Because of the nature of my job position I am privy to much of what occurs at the firm. I work with the manager as well as the managing partner so I know a lot of what could or should be confidential matters, matters that are kept from the other employees.

So, every Friday we do group lunches, which the firm pays for. We use this time to foster employee relations because our jobs don’t require much interacting. I think our lunches really help us to feel like a group instead of individual people doing their own thing.

However, one of our biggest clients is having a luncheon at Spago today, and the 2 partners, the manager and one very long term employee will be attending. Fine. It doesn’t really bother me. What does bother me is that the manager lied to me and said that these 4 people have a meeting to go to so do not order lunch for them. She straight-up lied. I know about the lunch at Spago because I was there when our clients were setting it up with the partners.

I know that I will be asked why these 4 people are not joining us for lunch. What do I say? Do I just straight-up lie to everyone’s face just as was done to me? Do I keep the secret I’m not supposed to know about anyway? How do I deal with knowing I have been blatantly lied to? It’s hard to trust people who you know will lie to your face.