'Grey's Anatomy': [SPOILER] Shows up With Shocking News

In the opening of Grey's Anatomy tonight, Meredith (Ellen Pompeo) teased a potential tragedy. During "Out of Nowhere," Grey Sloan Memorial Hospital was shutdown by a hacker. In the middle of the crisis, someone from Dr. Jo Wilson's past showed up.

All the computers stopped working suddenly early in the episode! The heart monitors flatlined, even though everyone in the ER was safe. Even the doctors' tablets stopped working.

It became clear that the hospital was hacked, with the hackers requesting 4,932 bitcoins for the encryption key. Miranda (Chandra Williams) tried to take control of the situation, just as the FBI showed up.

With everything down, Richard (James Pickens Jr.) told everyone to use pen and paper to keep track of patients. Other doctors were not happy with having to give out personal cell phones to keep in contact. And there was only one CT scanner that hadn't been hooked up to the network, so there was a long line to use that machine.

Miranda tried to get Jackson (Jesse Williams) to loan them the money. But the FBI insisted that paying the ransom — which could be over $20 million in real cash — would inspire other hackers to do the same at other hospitals. To make matters worse, the hospital lost its lights.

Meanwhile, the patients keep wondering what's going on. One woman has to give birth without the systems working, while one man is transferred to another hospital for treatment.

Schmitt (Jake Borelli) was in surgery with Meredith. He had to give blood to help save the patient.

Jackson and Maggie's (Kelly McCreary) helicopter ride to another hospital did not go well, with the patient starting to bleed out.

In the end, Paul Stadler (Matthew Morrison) showed up, and called Jo (Camilla Luddington) "Brooke"!

"Hey Brooke. Oh wait, it's Jo now?" he asked a stunned Jo. This was Stadler's first appearance in the show since the 23rd episode of season 13. He was Jo's abusive husband and it looks like Jo isn't her real name.

The big cliffhanger left us with the hospital still in crisis mode. The next episode doesn't air until Jan. 18.