Alright, Grey's Anatomy fans, after two weeks of wondering, let's cut to the chase: Did Derek (Patrick Dempsey) cheat on Meredith (Ellen Pompeo)? Ehh ... I guess it depends on your definition of cheating.

Here's Derek's story (which, honestly, is too simple to be true): His research fellow was the one who picked up his phone. Who knows why?! And he left it at the lab when he was on his way to the airport, and thus couldn't answer Meredith's calls. He flew back to Seattle because he realized he and Meredith had some things to work on.

But Meredith isn't buying it, thinking that Derek came back because he did something wrong and needed to fix it. After all, she was Derek's subordinate once upon a time, too.

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So then we start to get the real story. In a flashback, we meet Derek's research fellow, Renee (Scottie Thompson). And, as Meredith expected of the Other Woman, she is young and hot and has great hair (and great eyes, incidentally). There seems to be an instant spark between her and Derek the first time they're introduced, but maybe that's just the benefit of speculative hindsight on our parts.

Back to the present and Grey Sloan. Amelia (Caterina Scorsone) and Owen (Kevin McKidd) make awkward chit-chat in a scrub room while undressing each other with their eyes, and plan to meet up that night in hopes of getting some coitus sans interruptus. But it looks like their plans are about to get derailed: Owen's mother Evelyn is in the hospital after falling in the shower. And she's got her extremely handsome, extremely young, uniformed boyfriend, John, in tow. Owen takes immediate issue with their romance, noting that John is young enough to be his brother.

Elsewhere, Alex (Justin Chambers) introduces Meredith to a young liver patient named Danny, who keeps getting infections as he waits for a transplant. Meredith immediately suggests surgery, but Alex and Danny's sister would prefer a more conservative approach. And Jo (Camilla Luddington) is treating a patient who feels like she has a full-body headache. But, when Jo goes to wipe her "nose bleed," it retracts itself and she realizes it's actually a ... parasite? Worm? Whatever it is, it's horrifying.

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Maggie (Kelly McCreary), Alex and Callie (Sara Ramirez) all think it's a bad sign that Derek immediately hopped on a plane to come home. Obviously he must have something to apologize for, right? And they may be on to something. Another flashback shows Renee telling Derek that she wants to cure autism, which her little sister has. Much intense staring over microscopes ensues.

Amelia's getting some bonding time with Owen's mother as she performs a scan, with Mrs. Hunt confiding that she knows most people think of her and John's relationship as a joke, but she's having the time of her life. It's all very sweet and touching and a reminder that old people can find love too.

When Alex's patient Danny has another episode, he decides (to the great annoyance of Alex and his sister) that he wants to have the risky surgery that Meredith recommended.

Back to D.C.: After Derek sees Renee smash a coffee mug in frustration, she confides in him that she's been doing a research project for over a year with no results, and feels like she's wasting her time. Derek advises her that that feeling probably means she's close to a breakthrough. "Keep going. You're right at the line. You're going to cross it. Don't stop," he tells her, as she stares at him lustily. Excellent word choice, Derek. Really, top notch.

After her heart-to-heart with Amelia, Evelyn's bubble gets burst when Owen (after sweetly bringing her underwear and socks from the Grey Sloan Memorial gift shop) voices his concern that she's being taken advantage of. He stops short of saying there's no way a man like John could love his mother - but not before Evelyn gets the gist of it, and looks devastated. To make matters worse, when Amelia starts to gush to Owen about how great his mom is, he rather harshly tells her to "stay the hell out of" the situation.

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Jo has realized, after some probing, that there is indeed a "critter" residing inside her patient's sinus cavity. But, as she tries to lure the creature out of her patient's noise with some steam and tweezers, the patient - who's making a good play for Most Annoying Grey's Patient Ever, by the way - smacks her away.

And Alex and Meredith continue to snipe at one another as they're performing surgery on Danny, who ends up coding and dying - thus bringing an end to Meredith's streak, perfectly timed to Derek's return in Seattle. After they break the news to Danny's sister, Meredith blames Alex for doubting her and Alex gives her a hug, knowing that she's really just frustrated about stuff with Derek. (He's really getting the hang of this Person thing!)

Evelyn, meanwhile, has apparently taken Owen's words to heart. When John brings her some fresh clothes and a journal he picked up at the gift shop, she gives him the cold shoulder in return and starts to call things off with him - but then suddenly goes into shock because of a ruptured ... something in her stomach. Owen obviously panics, but later softens when he sees a heartbroken John sitting in the waiting room, saying he's not going to leave until he knows that Evelyn is alright. Which she is - but only because she was already in the hospital when the rupture happened. Owen finally warms up to John, who reconciles with Evelyn and tells her she looks beautiful even in a hospital bed.

Cut to the day before in Washington D.C. Derek calls Renee at 1 a.m. because he's "thinking about her research." He drags her out of bed (not personally) and down to the lab. They finally get a breakthrough, and an elated Renee tells Derek, "I could kiss you!" Derek halfheartedly says he needs to go, but doesn't actually leave and they lock lips in the lab.

And, if that weren't enough to make fans' stomachs turn, back at Grey Sloan, April (Sarah Drew) tells the sinus patient that the creature is eventually going to start chomping its way up to her brain, and she finally agrees to let Jo pull it out. Turns out it was a leech! Jo decides to name it Herbie and keep him as a pet.

Outside the hospital, Amelia (rightfully) yells at Owen for being a "jackass" and snapping at her earlier. Needless to say, she's not really in the mood to go on a date with him. But after learning that neither one of them is good with "surprises," they go back to Owen's place and finally do the deed.

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Then we see Meredith come home and, even though she (presumably?) doesn't get the whole truth from Derek, we do. He quickly aborted the kiss with Renee and ran out of the lab (leaving his phone - so he was sort of telling the truth). "I love my wife. I'm married," he tells Renee just before fleeing the scene. "I don't want anything other than what I have with her."

He and Meredith have a sweet vow renewal of sorts, with Derek saying that he mistakenly thought D.C. with everything, but Meredith is really his everything and he doesn't want to live without her. Meredith says that, while she can live without Derek, she doesn't want to. And they all lived happily ever after?

What do you think, Grey's fans? Should Derek have told Meredith about the kiss? Do you consider it cheating? And are you happy Derek is back in Seattle? Sound off in the comments!

Grey's Anatomy airs Thursdays at 8/7c on ABC.

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