S8, E12: Barney tells Ted that he plans to propose to Patrice and swears him to secrecy. This puts Ted in a difficult position, as he feels that he should tell Robin what's happening, so he asks her to be his date to the gala opening of the GNB building, intending to confide in her at the event. Meanwhile, Marshall and Lily have their first night away together since the birth of baby Marvin.