Chyler Leigh, Grey’s Anatomy Chyler Leigh, Grey’s Anatomy

On Grey's Anatomy this season, Seattle Grace and Mercy West are merging — meaning even doctors face getting not a scalpel, but the ax.

The hospital merger isn't the only problem the residents of Seattle Grace are having. When Thatcher Grey (Jeff Perry) returns, he throws the Grey sisters into turmoil, as Lexie (Chyler Leigh) fights to save her father's life and Meredith (Ellen Pompeo) doesn't care.

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On top of that, the 27-year-old Leigh tells that the budding relationship between Mark (Eric Dane) and Lexie has a wrench thrown into it. What else could go wrong? Plenty, she says:

Daddy Issues: "Thatcher comes into the hospital and is seemingly drunk," Leigh reveals. "There's this whole question where I'm saying, 'No he's not drunk, something else is going wrong.' Meredith sees him come into the hospital and goes, 'Oh, he's up to his regular antics again.' I have to convince her there's something else going on. You'll find out that he's got some really intense liver issues going on [and] he has to have a transplant."

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Sisterly problems:  What happens when dead-beat daddy returns? "Meredith is questioning whether or not she should even care [about Thatcher], and whether or not she should feel bad that she doesn't care," says Leigh. "Lexie got this whole and healed kind of a guy and had this really great upbringing. Meredith had an entirely different upbringing of neglect and abuse. It is like you're looking at two separate people. It stirs up some pretty big issues between the sisters and ultimately works out really well. Ultimately Meredith helps her, but not in the way that everyone is expecting."

Hospitals merging: In the first few seasons, the doctors "were really fierce with one another in trying to get cases and surgeries. That comes back this season," Leigh says. "There's an influx of doctors coming in [that] sends everybody into a panic, scrambling to make sure their job is secure. There are four doctors that come into the hospital that are some seriously fierce competition."

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Who's leaving Seattle Grace?  The hospital lost many staff members in last week's episode, but the layoffs haven't ended there. "Nobody is sure who is going to stick around. The people who you think are safe, might not be. The people that you think [are] totally going to be the ones to go, might not. It really throws a lot up in the air. Lexie, who tends to be a little more insecure about her abilities, she gets thrown easily with competition."

Lexie and Mark on the rocks: "Their relationship right now is pretty stable. They're making good progress, but there is definitely something that comes up soon that throws a wrench in the whole thing. They're coming up on some rough roads. As far as I've been told, it's pretty intense and I'm just hoping that they do [last]."

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Empty Hospital: With Pompeo out on maternity leave and Katherine Heigl leaving for a few episodes to film a movie, the hospital is going to be pretty empty this year. "Meredith is still in all the episodes," says Leigh. "They had to get pretty creative on how to give Ellen an out. With Katherine's Izzie being gone, it throws a lot on the plate for Alex [Justin Chambers] and how he has to deal with her being out. It certainly ups the drama factor. You'll see soon enough."

Are you worried about the state of Seattle Grace and its residents?