Los Angeles, May 4 -- The three leading ladies Meryl Streep, Emily Blunt and Anne Hathaway of the popular franchise "Devil Wears Prada" nod in agreement for the third installment only if the script is good.

"The script," Streep, 76, says immediately when asked alongside her costars for PEOPLE.

"A good script. It's all about the script," Blunt, 43, agrees.

"And then, everybody has to say yes," Hathaway, 43, adds, to which Blunt says, "It's got to be the core four." (Meaning the three actresses plus returning cast member Stanley Tucci, who happens to be married to Blunt's sister, Felicity Blunt.)The latest film sees Streep reprise her role as the imperious and impeccably composed Miranda Priestly, editor-in-chief of Runway magazine, while ...