Where on earth is Derek (Patrick Dempsey)? That answer was teased in the final scene from episode 20 of “Grey’s Anatomy,” when Meredith (Ellen Pompeo) was greeted at her window with the sight of flashing red and blue lights. This moment led viewers to believe that McDreamy might be McDead. But according to the synopsis for Season 11’s next installment, Derek is alive, well and -- a hero?

That’s right, according to the summary for “How to Save a Life,” Derek never made it to his meeting in Washington because he was a bit preoccupied trying to outsmart death. “Derek witnesses a horrible car accident and springs into action,” the synopsis for episode 21 reveals, confirming the reason behind Derek’s disappearance.

Meredith spent all of episode 20 worrying over Derek’s whereabouts -- especially when she learned that a plane had crashed in Seattle. That caused Mer’s PTSD to flare up, making her even more anxious to figure out where her husband was. Phew! 

In the promo video, Derek watches horrified as a car in front of him crashes and flips over. Thankfully, his occupation allows him to lend a helping hand to the victims (who all appear to be minors -- typical “Grey’s Anatomy” tugging at our heart strings!). In fact, one of those involved in the crash looks like “Parenthood” actress Savannah Paige Rae, who portrayed Sydney Graham in the NBC series.

“I don’t let people die,” Derek promises one of the victims, who is lying on the street, covered in her own blood.

The teasing trailer ends on an explosive note -- literally -- when one of the smashed vehicles bursts into flames. Looks like it’s safe to say episode 21 will be an intensely heated one!

Do you think Derek will keep his promise by keeping the car crash victims alive? Sound off in the comments section below with your theories on what will happen in episode 21, “How to Save a Life,” which will air Thursday, April 23, at 8 p.m. EDT on ABC.