Grey’s Anatomy season 12, episode 5 celebrates a major milestone outside the walls of the hospital when a simple dinner party takes a dramatic turn.

Happy 250, Grey’s Anatomy! Tonight’s season 12, episode 5, “Guess Who’s Coming to Dinner,” marks the 250th hour of the medical drama and founder of Shonda Rhimes’ TGIT. There is one notable difference between this monumental episode and the other special-must-see events the series has put on over the years — a majority of the drama will take place outside the walls of the hospital.

Related: Grey’s Anatomy 12×05 sneak peek: Ding dong ditch

The forgotten dinner party, hosted by the Lady Chief Sisters, goes on, but an unexpected guest forces both Meredith and Arizona to question whether extending an invitation to Callie’s girlfriend was worth the drama. Penny is not only the first person Callie has become serious with since the couple split, but she is also the nurse whose fatal oversight while treating Derek cost him his life. Only on Grey’s Anatomy, right?

The dinner party will not only be an emotional rollercoaster for Arizona, Penny, and Meredith, but April as well. Since Jackson moved out of their apartment, April has not ceased her mission to bring him back home. When she finally finds herself in a situation where neither of them can leave will her bold moves persist?

Some other interesting guests are tossed into the mix. Both Jo and Steph earn their invites into the inner circle, but so does the newest and palest intern. How did that happen? A notable missing intern, and Maggie’s current lover, may be the reason she suddenly excuses herself from the table.

Watch Grey’s Anatomy season 12, episode 5, “Guess Who’s Coming to Dinner,” tonight at 8:00 p.m. ET on ABC.