NOTE: Due to the unusual circumstances surrounding this crossover episode, we have recapped Private Practice and Grey's Anatomy together:

Addison, Naomi and Archer spill out of an ambulance at Seattle Grace. They rush Archer into an ICU room where he starts seizing because of a reaction to a drug they are giving him.

Derek orders them to stop the IV drip, and when Archer starts crashing, they order a crash cart to start his engines back up again.

Bailey has cleared her schedule to help support Addison. Derek exposits to Addison that her brother hates him, that he hated him long ago when Addie and Derek were still together.

Naomi sheepishly admits that she's sort of with Archer now, and Derek and Naomi chat awkwardly and incredulously about how their tight-knit medical school group has become so dysfunctional.

At home, Alex finds Izzie in full Martha Stewart craft heaven, making cards for her interns whose spirits are broken.

Alex suspects that something might be wrong with Izzie because she can't see the scissors that are sitting on the desk in front of her.

The interns are sullen and bratty about having to play a game with Izzie, but their competitive natures get the best of them.

Everyone has fun except for Sadie, who basically doesn't know any medicine. She doesn't know what a whipple is, or how to diagnose anaphylactic shock, or how to properly find the heartbeat of a fetus with an ultrasound.

Meanwhile, Lexipedia rules the scavenger hunt.

Pregnant aneurysm patient Jen was supposed to have her brain operated upon by Derek today, but because of Archer's emergency surgery, hers will be postponed until first thing in the morning.

Richard and Cristina have a patient named Michael who has colorectal cancer, but has been keeping his condition a secret from his daughter Beth.

Beth happens to be the blonde woman Major Hunt saw and freaked out over.

Apparently, they were engaged, but he broke up with her via a two-line email. This is certainly news to Cristina!

The old medical school gang sing songs that Derek apparently wrote way back when. Meredith didn't know about this.

Derek interrupts with the bad news that there is no way he can operate on Archer's brain without rupturing any of the eight cysts.

Privately, Addison tells Derek that after the divorce, she had to shrink him down to the size of a tiny, petty man, but right now, she needs him to be a god and fix her brother.

Sam decides to leave L.A. and follow the gang up to Seattle. He isn't quite sure why he is here, at the bedside of his ex-wife's boyfriend.

Meredith and Cristina briefly exchange some of the emotional turmoil each is going through, Meredith about not really knowing who Derek is, and Cristina about the revelation that Owen had a fiancée.

Owen finds Cristina and tells her that she can ask him about his engagement, but she has no interest in any of that.

She keeps things strictly professional.

Unfortunately, the woman happens to be in the hallway and sees him. The back story is that she believed him to be in Iraq this whole time, and she had been praying every night for his survival.

He hasn't even told his mother that he is back in the U.S.

Addison goes to the hospital chapel, while all of her friends stand around in the doorway trying to figure out what she's doing.

Callie jumps in to talk to her and tells Addison about her recent conversion to ... well, you know, by praying to God about how she doesn't know what to do about the cute, perky and incredibly hot surgeon she kissed.

Sam pops in on Derek to tell him Addison is praying. The two old friends catch up for a bit, with Sam asking if Meredith is a midlife crisis. (The answer is no.

Archer doesn't want to go through with the surgery, but Derek calls him a coward.

As Derek begins to operate, tensions are high but he appears loose.

Major Hunt's patient Michael starts coughing up blood, and they rush him into emergency surgery. His ex-fiancee is there and wants to know what's going on, but Owen won't tell her, according to Michael's wishes.

In surgery, they find a big tumor, which means he'll have to start getting chemo. But even then, Owen says Michael won't want to tell his daughter.

Her mother died when she was little, so he has been sheltering her ever since. Cristina is adamant, however, that she deserves better.

In Archer's surgery, Derek has successfully removed seven cysts and seven worms, but it's the last one that gives him trouble.

The cyst bursts before he can get it out, and the worm wriggles out and down into his brain. Archer starts coding, but instead of working to shock him back to life, Derek wants to find that worm. He does.

The intern game is almost over, and Alex and Izzie construct a finish line tape for them to race toward. Izzie again shows sign of some visual impairment, having trouble grabbing the roll of tape from Alex.

Lexie is declared the winner because she is the only one who has the correct final diagnosis from the scavenger hunt.

Owen finally decides to tell his ex that her dad has cancer.

Meredith and Cristina watch Derek and his friends laughing and celebrating Archer's successful surgery. Meredith rues the fact that she doesn't know this laughing, singing, guitar-playing social Derek.

Owen finds Cristina and explains that he calls his mom once a week, but pretends that he's still in Iraq. He can't bear to tell her he's back.

She'll look at him like a ghost, he says, and the only time Owen doesn't feel like a ghost is when he's with Cristina - she sees the real him.

George observes throughout the intern game that Sadie doesn't know a damn thing about medicine. He offers to help her get up to speed.

She huffily walks away, saying that she doesn't need a tutor, but George calls after her that she could hurt someone seriously.

Later, he gives her the ultimatum that either she turn herself in to Richard for being a liability with patients, or he will. Sadie chooses to quit the program because she would rather be a quitter than a cheater.

Apparently, she faked her way through medical school and was hoping that if she got into Seattle Grace, Meredith would be able to keep her afloat.

Sadie wants to go to Europe with Mer like they did after medical school, but Meredith reminds her she has a job. Guess that's the end of Sadie.

Mark professionally congratulates Lexie on winning the intern game. Addison watches and deduces that they are sleeping together.

She almost outs them to Derek, but Mark saves himself by blurting out that Derek is planning to propose to Meredith.

Derek finally shows his face to Jen and promises to schedule her for first thing in the morning. But she begs for him to do it now, so he does.

At Joe's, Addison thanks Derek for being a god, but says that he's going to have to become tiny again and go back into his little box.

Everyone sings an old song that Derek wrote for Addison in med school.

They drink and celebrate, but Derek gets paged as Jen has complications. The whole gang follows him to the hospital, thinking that it's Archer.

Alex tends to Jen who is having trouble breathing.

In Archer's room, Sam passes out from an asthma attack, leaving Naomi torn about which man to check on.

Richard wants to publicize Archer's surgery and call in some newspapers.

Archer isn't quite sure that Derek got everything because his vision is blurry, his head hurts and the room is spinning.

He wants another CT done. Richard orders Bailey to do the CT but doesn't tell Derek about it.

Derek is also preoccupied with Jen, so he asks for Addison's advice on how best to treat her. Addison does an ultrasound and finds out that the baby is anemic.

Sometimes the mother mirrors the baby's symptoms, and in Jen's case, the baby's anemia is causing congestive heart failure in both of them.

At home, Alex asks Izzie what's wrong because he has been noticing some visual impairment in her. She distractedly says she's fine.

Bailey treats Sam for his asthma, and wonders how a woman like Naomi can go from a hunk of a man like Sam to someone as ... well, Archer.

There's evidence of some bad complications going on with Jen, and as Alex and Addison look at the test results, he asks her for advice on whether he should run away to a different city like Addison did.

He tells her he's with Izzie now, and while he loves her and wants to be with her, but he knows that she's all sorts of crazy.

Addison orders more tests for Jen, and when Derek finds out he gets very angry. He yells at her that this is his hospital, Jen is his patient.

Naomi confides in Addison about whether she's crazy to jump in so quickly with Archer. Naomi asks Bailey how Archer and Sam are doing, and Bailey gives her a whole barrage of yelling, classic Bailey style.

However, Mark shows up and tells Naomi that she and Archer being together gives him hope that things might be real between himself and Little Grey.

When Derek nicked her aneurysm during her craniotomy, she lost a lot of blood and had to have a transfusion.

But for some reason, the baby is not accepting the blood, and mother and baby are going into heart failure.

However, even if they do deliver, the fetus is only at 24 weeks, which doesn't give it very good odds of surviving.

Addison and Derek give the bad news to Jen, but she wants to leave the baby in for two more weeks. Without consulting Addison, Derek says that they can perform an in utero blood transfusion, which Jen wants to do, despite Addison's assertions that the risks for both mother and baby are high.

Derek blames himself for Jen and the baby's conditions because he was the one who nicked her aneurysm in the first place. If either dies, it will be his fault, so he begs Addison to do the in utero procedure.

She agrees. Throughout the surgery, Addison bickers with Derek about how he cornered her into doing the operation just like that time, years ago when they were married, he cornered her into making the Thanksgiving turkey.

It turned into a disaster, and his sister got salmonella. Derek emerged the hero of the fiasco by making hot dogs for everyone.

Fortunately, they save both Jen and the baby, so they are both heroes in this case. While they are cleaning up, Derek admits his mom hated her all these years, which is why she never gave him her engagement ring.

It turns out that Sam needs a special inhaler because he's allergic to the regular kind, and that's why he had the asthma attack.

Richard and Naomi bring the CT scans to Archer, who reads his own scans and sees more cysts. He thinks he's going to die.

Mark comes by to see if anyone wants to go to the bar, but everyone is sad because they think Archer is dying again. Archer apologizes for sleeping with everyone's girlfriends, for wrecking Sam's car and leaving Naomi, whom he has feelings for, alone after he dies.

He goes overboard, crying and carrying on, until Derek storms in.

He barks that Archer didn't read the CT scan correctly. The spots he saw are fluid collecting in the spaces where the cysts used to be, which is normal.

Derek says that not only is Archer not dying, but he will continue being an ass like he always has.

Bailey and Sam watch Naomi and Archer through the window. Bailey announces that she is going to go home to her husband, with whom she has been having problems with lately, and hug him and kiss him and thank him for all the things that she sometimes forgets to thank him for.

She doesn't want to end up in Sam's shoes, looking through a window at his "ex-life."

Looks like everything has gone well with Jen's surgery. The baby's heartbeat is strong. But when Jen comes to, she starts spouting nonsensical words.

So, the baby is healthy, but the mom's brain is not. Addison did her part, but Derek's part of the deal is left in doubt.

Meanwhile, in L.A., Cooper has a very sleep-deprived new mom named Rachel who brings her baby in after it slipped in the bath tub. Cooper, Violet and Pete all determine that Rachel is suffering from psychosis due to post-partum depression.

Violet thinks that they should keep the mother away from the baby while she is treated for her psychosis, but Pete argues that Rachel stopped herself before any real harm came to the baby.

He thinks that bonding with the baby may keep her grounded and speed up her recovery.

They are arguing about this because Pete may be the father of Violet's unborn child, and he's angry that she isn't letting him in or telling him anything.

She thinks she's doing what's best for the baby, but he thinks that having a father is what's best for the baby.

Meanwhile, Charlotte tells Cooper that she gets that Violet is his best friend, but Charlotte is supposed to be his best friend.

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