Raj can't host this year's Christmas Eve dinner party because his soon to be divorced father is coming for a visit. So Amy volunteers to host the dinner, she choosing the theme of a traditional Victorian Christmas. Raj and Dr. Koothrappali are nonetheless invited. The day of the party, Leonard and Howard, working on an experiment in the clean room, are detained and require Raj's help when an accident causes the clean room to be not so clean. They have to figure out what to do, the three ultimately deciding that the blame falls on one person, who has a sense of déjà vu for the remainder of the evening and as they deal with the issue. Bernadette is driving Sheldon to Amy's. Irked that Amy would agree to host a dinner that he wants no part of, Sheldon tries to figure out a way to get back at Amy. That leaves Amy, Penny and Dr. Koothrappali alone at the party, which is dominated by Dr. Koothrappali's less than positive current view of marriage, and Amy's focus on making everything as traditionally Victorian as possible.