Captain Burnham and the U.S.S. Discovery are sent to retrieve a mysterious 800-year-old Romulan vessel; until the artifact hidden inside is stolen, leading to an epic chase. Meanwhile, Saru is offered the position of a lifetime, and Tilly’s efforts to help pull her into a tangled web of secrecy.
Trek Central has also provided a picture of what is probably the Romulan ship described in the synopsis.
Also, TrekCore has compiled some shots of what appears to the be interior: