The truth will soon be revealed, or at least that’s what the promo video for the coming installment of “Grey’s Anatomy” suggests. According to the episode 17 trailer of the hit ABC drama, Derek (Patrick Dempsey) will finally explain to Meredith (Ellen Pompeo) why a mystery woman with a perky voice answered his phone. But it looks like Mer won’t be buying into his tall tale.

“I came home because we’re in trouble,” Derek reveals why he rushed home from D.C.

“I wish I could believe you,” Mer responds. And as it turns out, she's not the only one skeptical about Derek’s return. Both Callie (Sarah Ramirez) and Maggie (Kelly McCreary) will question Derek’s motives in the episode, titled “With Or Without You.”

“A woman answers his phone. He immediately gets on a plane and shows up in the middle of the night,” as Callie recalls the suspicious events. Maggie theorizes that Derek must have flown back to Seattle to apologize. “Because he has something to apologize for,” Callie concludes.

Seems like these girls must have had a change of heart because in episode 16 the two both claimed they were on Team MerDer. They even tried to calm down their distraught friend by telling her there was no way Derek could have betrayed her. Maggie then suggested the far-fetched scenario that maybe it was a nurse who answered Derek’s phone while he was in surgery. But it wasn’t a nurse who picked up his cell -- it was Derek’s resident, Renee Collier, played by “Skyline” actress Scottie Thompson.

In the promo video, viewers can see Renee cozying up to her superior -- even attempting to locks lips with Mer’s spouse. But the trailer cuts before we can see if any damage is done. The synopsis for episode 17 states that Meredith will try to “figure out what to do about Derek” after getting rattled by his alleged infidelity.

Meanwhile, Owen (Kevin McKidd) "is shocked when his mom is admitted to the hospital,” the summary concludes. Heads up, Amelia (Caterina Scorsone)! You might be meeting the mother of your boyfriend sooner than you thought.

“Grey’s Anatomy” will air episode 17, “With Or Without You,” on Thursday, March 26, at 8 p.m. EDT on ABC.