The Big Bad will be Dame Helen Mirren. She is playing . . . The Progenitor.
An alien ship commanded by The Progenitor / Dame Helen Mirren the size of Texas drops out of warp above Earth and DECIMATES a quarter of Earth's land mass* (decimate may or may not be used correctly in this instance - but it sounds impressive). France and Chateau Picard are caught in the assault. Fortunately for Picard he was in London auditioning for a part in The Royal Shakespeare Company** (audition scene included at the insistence of Patrick Stewart).
After her bloody assault, she sends a cryptic message to SF Command requesting Picard meet her in the former Neutral Zone. Picard, shaken and overwhelmed by these staggering events, calls his old crew up to accompany him on One Last Mission™.
On arriving in The Neutral Zone, she will be revealed to be. . . the Mother of Khan - and all the original genetically altered Supermen.
She will also reveal that. . . Picard ancestry can be traced back to her. Yes, Picard is related to Dame Helen Mirren / KHAAAAN.
Dame Helen Mirren will go on to explain it was his latent genetically engineered DNA that facilitated his successful mind transfer to the Golem body (GENETIC ENGINEERING IS ILLEGAL NOW AND FOREVER, HENCE WHY THIS TECHNOLOGY FELL OUT OF USE IN THE DISTANT FUTURE BECAUSE IT ONLY WORKS IF YOU HAVE MAGIC BLOOD - WOAH).
Dame Helen Mirren will then go on to reveal her dastardly plot - she wants the Golem technology for herself and her legion of Supermen (who are mostly still in cryonic suspension for reasons - only a few of the men are awake to man the ship. They are muscular, shirtless & glistening.). But unlike Picard, she wants more than a second chance at life; she wants IMMORTALITY.
But, the Golem technology / research has been classified and is beyond Dame Helen Mirren / The Progenitor's reach. Her plan? Lure Picard into TNZ, KIDNAP him and unlock the secret to human-to-android mind transfer.
*Why did Dame Helen Mirren need to blow up a quarter of the Earth's surface to progress her plan? This story is going to be so awesome and fast-paced you're not going to care. Plus, a quarter of the planet blowing up is going to look wicked cool.
**If France is wiped out, won't London also be taken out? Again, this story is going to be so awesome and fast-paced you're not going to care.