The cast of the Grey's Anatomy spinoff starring Kate Walsh and Taye Diggs is really clicking, Diggs tells PEOPLE.

"They're great. We have really great chemistry," Diggs, 36, said of his castmates Thursday at the opening of the new club Runway in New York City.

The initial episode has "just finished" filming, he said, "and we're hoping people dig it."

ABC plans to test out the show with a "back-door pilot," an expanded two-hour episode of Grey's, Reuters reported in February. No air date for the episode has been set.

Diggs, who said he plays a "general practitioner" on the show, was coy when asked if he could reveal any key plot details.

"Plot what? Secrets?" he said. "I can't tell you! It's a secret."

Grey's creator Shonda Rhimes is writing the first episode, which, according to USA Today, will feature Kate Walsh's character, Dr. Addison Shepherd, mulling an out-of-town job offer.

Labels: Taye Diggs