Before Grey’s Anatomy season 12 returns this Thursday, refresh your memory with 11 key developments to remember from season 11.

Looking back, Grey’s Anatomy season 11 tackled some of the heaviest material in the show’s history. Inoperable tumors, the loss of a child, the arrival of another long lost sibling, and the death of one of the show’s most beloved characters. Grey’s Anatomy season 12 will take on a much lighter tone, but before we get there let’s look back at 11 key plot points that occurred in season 11.

1. The carousel keeps spinning

Meredith Grey’s past crept into this season and refused to let her move forward. As the show kept spinning, Meredith watched her marriage fall apart, come back together, and get ripped away just as she tried to jump off. She battled alone at work, at home, and finally accepted that she was not alone in her fight. As season 12 makes its debut, she must fall back on those she finally came to appreciate in season 11 — her friends and surrogate family at Grey Sloan Memorial.

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2. Arizona and Callie are separate but happy

The first half of the season saw Callie and Arizona trying their best to fix their marriage. No matter how much glue their therapist offered, it did not stop new cracks from appearing. Their decision to end the marriage was not easy and the fallout lasted through the remainder of the season. It was awkward and painful, but eventually it got easier for both parties to move forward.

3. Tumors, tumors, and more tumors

Grey’s Anatomy season 11 needed a bingo card for tumors. From young girl with an abdominal tumor that made her look pregnant, to Dr. Herman’s brain tumor, to the tumor that took hostage of a patient’s lungs and heart, you could check off three major ones in under three episodes. Each tumor gave a doctor the opportunity to rise above a challenge and prove something to not only themselves, but those around them.

4. Alex and Jo’s roller coaster love affair

It’s on again, it’s off again. We needed a patient chart for Alex and Jo’s relationship last year in order to keep track of whether these two were making up or breaking up. At the close of the season, Alex invited Meredith to move back into Ellis’ home forcing Jo to make a drastic decision. If they were going to stay together, they needed to live alone. Let’s see how domestic life treats Karev and Wilson in season 12 when they don’t have someone walking in on their showers.

5. Watch out for the rise of the residents

Jo and Stephanie fighting for hours in each specialty brought back an element of Grey’s Anatomy that was absent for quite a while. Watching the doctors struggle to learn from the first batch of doctors we met, hopefully opened the door for more opportunities to tell similar stories in season 12. Jo lucked out when it came to the strange and unusual cases that often led to time in the OR. However, Edwards’ time grinding in the ER and on the service of many doctors primed her to take on the latest batch of interns.

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6. The new Shepherd in charge

Aside from losing her brother at the tail end of the season, Amelia Shepherd had quite the year at Grey Sloan Memorial. In the wake of Derek’s departure to Washington, D.C., Amelia took over his post as Chief of Neurology only to have him return and challenge her every decision. But after she took on Herman’s case and gave her a second shot at life, Amelia proved that she is a force to be reckoned with. However, that force was too much for Owen to handle and broke off his romantic entanglements with her. When Derek died, Amelia was left with no one to turn to since her sister-in-law not only made the decision to pull the plug without talking to her, but took off to live alone for nearly a year.

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At the close of the season, Amelia found herself back in the good graces of Owen and her sisters, and found some closure with Derek’s death.

7. Bailey is fighting to be the new Chief

After taking the board seat unanimously from Alex Karev, Bailey’s minor victory in Grey Sloan took a backseat to her new goal, winning the position of Chief of Surgery. Richard is finally ready to move on as the interim Chief after Owen stepped down. Bailey’s successes are typically above board, but this season saw her breaking into her locked genome lab to continue some disbanded research. Although it led to the discovery of a genetic heart disease, Bailey is more often than not willing to step over the line to get the best outcome.

On the other hand, she has a stare that casts fear into the hearts of many.

8. Jackson and April are fighting a war

The heaviest story of Grey’s Anatomy‘s 11th season was certainly April and Jackson’s tale of loss. Their decision to give birth to their son who died mere hours later took every ounce of the strength the couple could muster between them. Jackson returned to work and did his best to give April everything she needed, but what she required he never truly understood. While April suffered in silence, working harder than she ever did before, Jackson struggled to sort through his grief without her.

Finally, April took Owen up on an offer to go overseas and serve with the Army. But one tour turned into multiple extensions and eventually April chose another tour of duty over staying with Jackson.

9. Letting Derek go

Is it okay to talk about this yet? This wound ranks high on the scale of pain Grey’s Anatomy fans had to endure. Just like George O’Malley, Mark Sloan, and Lexie Grey’s deaths, Derek’s departure outraged, devastated, and confused fans across the world. After a season watching Derek and Meredith finally get past 11 seasons of fights, breakups, makeups, births, deaths, and post-its, the end of an era hit viewers hard.

10. The Maggie era

Maggie’s arrival this season brought less turmoil than Lexie’s appearance, but required some adjusting on Meredith’s part. Her new half sister was not some intern that she could get away with punishing, Maggie had rank on her side as an attending. Their relationship quickly moved beyond petty fighting and the focus shifted to Maggie and Richard trying to form a bond.

11. The interns are coming

In the Grey’s Anatomy season 11 finale the new interns flooded the hospital as Richard offered them his introductory speech, their right of passage. But there was one intern who was running a bit late and decided to take on more than he could chew on day one. Be sure to watch Andrew DeLuca and his friends in scrubs usher in a new age of Grey’s Anatomy in season 12.

Grey’s Anatomy season 12, episode 1, “Sledgehammer,” premieres Thursday, September 24 at 8:00 p.m. ET on ABC.