Arizona supports Callie, Karev steps aside for Meredith, and Christina competes with Jackson.
Meredith watches as Derek operates on a clinical trial patient with Karev by his side. When they emerge, Meredith tells Derek the clinical trial was open to all of the residents except her! Derek and Alex go to check on another Alzheimer's patient, Daniel. The wife wonders if there could be a full reversal with the trial drug. Derek gives her hope. When Daniel has an episode of memory loss and calls out for someone other than his wife, Meredith steps in to help. The woman he fell in love at the 'home' is brought in - they don't know their spouses. Daniel's wife asks Karev to give him the drug, even if he's supposed to get the placebo. Karev is stunned, and uses Meredith as a sounding board. He realizes how suited she is to the trial.
Mark and Callie lay together in his bed and discuss her being pregnant. He's thrilled, until he remembers that he has to tell Lexie. Callie goes over to see Arizona, who is still shell-shocked that Callie slept with someone else after they broke up. Callie tells her she has to plan for the baby, and she wants her to be part of it. Arizona says, "I'm in."
Webber and Lexie are in the OR when he first hears that students are following Bailey on Twitter. Webber catches up with Bailey, who describes why Twitter is a great teaching tool. He orders her to shut it down. She counters that he doesn't understand it. She gives him 'Bailey eyes'. He says he'll look into it. Bailey goes back into the OR, and winds up with Lexie in there pleading with her not to leave Twitter. Bailey muses that Webber wouldn't know if she kept tweeting.
Teddy lays out a case. Christina grabs the file and takes off with Jackson in pursuit. Teddy moves on and Arizona corners her. She tells her that she might be having Mark Sloane's baby, and then explains. Teddy goes to see her patient. Jackson and Christina are in the room competing to give superior patient care. Teddy sighs. Christina and Jackson continue to compete until Christina tells him the advice she's giving the patient isn't about that. When Jackson brings up Christina's PTS, Teddy winds up angry at him. He follows Christina to apologize - she pretends to be breaking down. When he goes to find Owen, she grins at Meredith, saying she will be doing the surgery. After Christina assist Teddy in surgery, Jackson tells her, "Bite me, Yang."
Callie catches up with Mark in the corridor at Seattle Grace. She tells him he could be the baby's 'cool uncle'. He asks her never to say that again - he's the dad. She tells him to tell Lexie then, sometime before the baby comes out looking 'Sloane-y'. Callie and Mark head to see the OB/GYN and Arizona joins them. Callie is on edge since she's been bleeding. The doctor meets the lesbian lover and baby daddy, and then tells Callie she's fine.
Mark catches up with Derek and blurts the news about Callie having his baby - and Lexie wanting a child about as much as a root canal. Instead of advice, Derek wonders how he's so fertile when Meredith wants a baby and can't have one. Mark is paged back to the OB/GYN's office - Callie hasn't left - she won't take any chances with the baby. Mark winks at the doctor and suggests a scan. Callie winds up freaking out and Mark yells at her. She admits she's terrified of messing up with this baby. Mark holds her. They get an ultrasound and she sees the baby and hears the heartbeat.
In his office, Webber is valiantly trying to master Twitter with Owen's help. He finally gets on Bailey's page and sees that she's tweeting during her surgery. He rushes into the OR and orders her to stop. Lexie keeps tweeting as the patient has a crisis. The solution to save the man's pancreas comes over Twitter. Webber unwittingly gets sucked into answering questions on Twitter and connects with a former resident, which impresses him. Soon, he's talking faster than Lexie can tweet.
Daniel, the Alzheimer's patient has surgery, but comes out of it asking for the woman who isn't his wife. Karev asks the wife to give whatever she can. Derek tells Karev he did well, but he credits Meredith, saying she should be on this trial. Derek catches up with Meredith and tells her she's on the trial as of tomorrow.
Bailey goes to Webber's office to discuss tweeting and finds he's become addicted - even telling her what to tweet on his behalf tomorrow.
Arizona opens Callie's door and moves her things in. She angrily informs her that they are together because they love each other. Arizona refers to the baby as hers, and they kiss.
In Mark's apartment, Lexie is cooking. He blurts that Callie is pregnant. Lexie says it's great and asks if they did the turkey baster thing. Mark admits the baby is his. Lexie is furious, and leaves.
Spoilers for Next Week on Grey's Anatomy:
Lexie goes crazy when her and Meredith's father shows up at Seattle Grace with a much younger girlfriend!
While there was nothing outstanding on tonight's episode, I enjoyed the clinical trial stuff with Karev, Derek, and Meredith, as well as the baby storyline with Mark, Callie, and Arizona. I love that Arizona is 'being there' for Callie. As for Lexie, her reaction was every bit as selfish and immature as I expected - I SO want to see Mark with someone else! The Twitter plotline was really good too - made me grin to see Webber go from grudgingly 'checking it out' to an avid tweep. So funny! I also liked the new OB/GYN doctor - hook her up with Alex! Jackson is still a whiner...that's it for tonight! Be sure to share your comments with me in the section below.