Tonight's Grey's Anatomy is all about invasion, the influx from Mercy West, and the new docs are definitely not out to take prisoners.

The merger gets off to a rocky start when cocky young Reed (Nora Zehetner) refuses to take her stuff out of George's old locker, almost causing a throwdown between her and Izzie.

Due to the sheer volume of cases in the hospital, the Seattle Grace and Mercy West doctors are paired up and assigned "zones" - an idea from one of the newbies - to handle the mob scene.

In said zones, one of our favorites frequently feuds with an invader.

The cases are almost secondary this week, used as props to showcase how the new Mercy West gang are one-upping the Seattle Grace crew at every opportunity.

Lexie and Mercy West's April (Sarah Drew) work together on the case of a burglar injured during the act, leaving him with a broken back.

When Lexie is one-upped by the conniving April on the suggested course of treatment, her patient helps her out by stealing April's notebook.

In this notebook, Lexie discovers not case notes but self-pep talk notes April uses to bolster her flagging self esteem.

Lexie cruelly uses the knowledge to tear April down, but immediately feels bad about her actions. She ends up apologizing to April, even if she admits she still dislikes her. But she went over the line and she knows it.

Cristina and newcomer Jackson are working together to save a man stabbed by his friend for having sex with the friend's 19-year-old daughter.

Although Cristina technically saves the patient's life by fixing the stab wound, Jackson gets the credit for doing some heroic tackling when the patient is threatened again by his hammer-wielding friend.

Cristina ends up in a crying fit in Meredith's hospital room (Mer is exempt from the drama, probably to her benefit) over the downward spiral of her career.

She felt alive when she was working with Burke and holding hearts in her hands every day. Now she feels none of that, she just feels lost.

Alex and Mercy West partner Reed spend the hour fighting over a man with both an adrenal mass and carotid stenosis.

Alex and Reed are extremely antagonistic from the start, going so far as to argue about care in front of the patient and his daughter (Kathleen Wilhoite).

In turn, the daughter rightfully yells at them and snaps them out of it... for about 30 seconds until they start up again.

Izzie and Mercy West's Charles (Robert Baker) get paired up on Sarah, a young woman in desperate need of a kidney transplant and down to her last access point for dialysis.

They seem to be getting along swimmingly until Izzie overhears him bragging to his Mercy West friends about her being his "surgical bitch."

In the midst of their troubles, Izzie almost kills patient Sarah by ordering a bad procedure and causing her to code.

Bailey manages to save the patient, but because of her troubles she will lose her chance at the transplant kidney she's been waiting years for.

Bailey is not done fighting for her, though - she brings her to L.A. and Private Practice later in the hour! Woo hoo!

But back to Seattle Grace. Chief has to get down the the business of firing people, and HR insists he use a specific speech because the last person he fired (the pregnant intern) is suing for wrongful termination.

Who's getting the ax? Izzie. She can't believe she was allowed to come back after the LVAD wire incident, but Richard says this is a different era.

She takes it extremely hard, to the point where she skips town and leaves Alex via a note taped to his locker.

Alex cries to Meredith and Cristina that she's left him. No other explanation offered or needed.

Meanwhile, one of the few doctors with job security (after last week's promotion to attending) has her own drama to deal with.

Callie's dad shows up wondering why they don't talk anymore. Turns out he's only there to "pray away the gay" from Callie, complete with his priest in tow for support.

Callie is disgusted, but Arizona urges her to cut him some slack since her news was so shocking. They sit to talk, but her father tries to use God to show Callie why her lifestyle is wrong.

Fortunately, Arizona talks to Callie's father and makes him see that Callie is still the same person, the person he raised. This makes him see the light, and he makes amends with Callie in the end.