5 second plot: Robin's mom arrived at the wedding. She wants to meet Barney. But he's out solving a mystery with the boys. Apparently Lily is hiding a big secret.
5 second review: Why would Lily not tell her husband her secret? That seems weird to me. Aside from that, this was a pretty good episode with some great old familiar faces. Only 2 more episodes left! It feels very strange that it's going to end soon.