“Data’s Day”
When Keiko Ishikawa tells Data she would better call off her wedding with Miles O’Brien, Data thinks it would be a good idea to tell O’Brien. Of course, O’Brien is not really glad about it. The Enterprise meets with a Warbird in the Neutral Zone, where Federation Ambassador T’Pel is supposed to negotiate with the Romulans. T’Pel is killed in a transporter accident. After a closer examination it is assumed that the accident was a ruse and T’Pel was actually abducted by the Romulans. The Enterprise follows the Romulan ship, only to learn that T’Pel is a Romulan spy whose real name is Selok and who has returned home. The wedding takes place as scheduled. summary by Ex-Astris-Scientia
It’s been some time since I saw this one but I must say I loved it. I guess it’s no big surprise for anyone who’s read any of my comments 
The dancing scenes are hillarious! I mean, Data is just so disarming and innocent. I am not a particularly big fan of Keiko / O’Brian thread (had too much of it in DS9 IMO) but that was brand new. Adorable.