Leonard and Howard are working in a clean room on a project when a pigeon flies into the room contaminating it. They try unsuccessfully to get the pigeon to leave. They call in reinforcements, a.k.a. Raj, to help. The three scientists can not figure out what to do. They come up with one idea, but it doesn't end out quite like they expect.

Howard will never look at a bird the same way. In the end, it's Penny who comes up with the solution to their problem, so they can head over to the Christmas celebration.

Raj's parents are going through with their divorce and Raj's father shows up for Christmas. Amy offers to host a Victorian Christmas and invites the friends, including Raj's father. Penny ends up entertaining him when Raj heads to the lab to help Howard and Leonard.

Bernadette drives Sheldon to Amy's house. On the way there, he decides to get Amy a present against their decision not to exchange gifts. His plan backfires when she loves the gift and has one of her own for him.

It's a lovely Christmas gathering with plenty of laughs.

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