Suzi, you're so funny!
Well, I wrote out story lines for two sequels to Under Seige a while back.
US3: Casey Ryback has been out of the Navy Seal business for 10 years now. He's still running the Mile High Cafe in Denver, and has done his best to raise his neice on his own. She's just finishing up her post graduate studies, is moving to Washington and is getting married. She comes to visit him in Denver, to talk to him about the wedding, which he and his staff are catering, and is worried about what he's going to do without her to look after any more.
The cafe is closed for renovations at the moment; she catches him as he and his staff are loading a truck - he's been asked to cater Admiral Bates' retirement dinner, which is being held in a small, isolated place outside of Denver at a conference centre housed in a mansion that was built by an eccentric millionaire in the early 20th century.
Casey and his staff arrive at the conference centre and take over the kitchen. Unbeknownst to them, however, in addition to Admiral Bates' function is another function, a conference on limiting biological and chemical weapons, attended by stakeholders from all over the world, including military specialists, scientists and a former first lady (just for fun, played by Stockard Channing as "Mrs. Bartlett"). Mrs. Bartlett's Secret Service detail includes one female agent (okay, I can dream, can't I?).
What no one knows, though, is that this conference centre is a front for the CIA, and is, in fact, connected to a concealed lab where samples of just about every kind of biological and chemical agent are stored, supposedly, securely. No one is supposed to know it's there - but someone does.
While Casey is cooking up Admiral Bates' dinner, (apparent) terrorists take over the conference centre above, and they do it first, by quietly taking out all of the security people one at a time, and substituting carefully disguised "lookalikes", and then by staging an attack by masked operatives. The female Secret Service Agent figures out something is amiss when she comes back from the ladies room (even agents have to pee) and when she's spotted, ducks back into the ladies room when they give chase. There's a chute she pulls herself into and the slide down lands her in what used to be the laundry room and is now... the kitchen!
The doppelganger agents go down to the kitchen and try to convince Casey to turn her over, only he's not buying it - he knows the agent the fake agent is supposed to be and he realises something's up.
Fighting ensues. Bad guys dispatched.
Casey gets his people loaded up in the truck and persuades them to leave him behind. He tries to the get Secret Service agent to go too, but she's not having it. Her job is to protect the former First Lady, and she means to do it, or die trying. She trades clothes with the female bad guy who just happens to be her exact size - she realises that this woman was supposed to have replaced her, as well. She wonders if the replaced agents are all dead....
Casey and the agent go off to figure out what's going on, and how to fix it.
Turns out that the agent's great grandfather was the one who built the mansion, and she knows all its secrets - the great grandfather was apparently a very eccentric fellow who didn't like seeing servants, so he built secret passages all over the mansion so that the servants could pass from room to room and he'd never see them.
The bad guy turns out not to be a terrorist, but somebody who used to work for Tom Breaker (poor, twitchy Tom Breaker!) and who got passed over for promotion too many times. This was both revenge against Breaker and the CIA as well as the opportunity to make a tidy sum of money.
After much sneaking around and eliminating of bad guys, as well as attempts to free the hostages which have been locked in various of the mansion's rooms, they manage to call for help (regular lines of communications had been severed, of course!), but not before they find out that the mansion is rigged to blow up. Agent does her job and rescues the First Lady and turns her over to the cavalry when they arrive; but refuses to leave Casey behind on his own and goes back into the mansion. They follow the bad guys down to the secret storage facility, and bad luck catches up with them - the agent gets caught, but Casey doesn't. Tom Breaker is there, as hostage. The agent doesn't crack, but Breaker does, about who else has possibly been gumming up the works.
Agent is bundled into a Hummer with Breaker and a bunch of the bad guys and this vehicle leads a convoy of small vans with the goods loaded in them. Meanwhile, Casey has been following them along a catwalk.
Agent in the Hummer, once the vehicle gets outside, gets physical with her captors. Casey has blocked the exit enough so that the trucks will have trouble getting out, which buys him time. He jumps onto the Hummer and yanks Breaker out of the vehicle to get him out of the way, and then deals with the driver. Casey and the agent jump out of the moving vehicle which then crashes, spectacularly, into the side of the canyon they're in.
Casey, muttering, "I'm getting too old for this ****," gets up and looks around for the agent, who he spots lying some two dozen yards away, not moving. Hobbling a bit, he goes over to her, checks to see if she's all right, which she is, except for her injuries. He helps her up, and they discuss going in and dealing with the trucks, but the cavalry has shown up, and they decide to leave it to them. They wander off together, arguing about who had more scars and injuries.
End scene: niece's wedding. Niece is dancing with her husband and is still worrying about what Uncle Casey is going to do with himself after she's gone, when husband points to Casey and the agent, deep in conversation and um, other things.
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I'm almost embarrassed to have shared this, since this, in writing circles, is what's known as fanfic of the Mary Sue variety, in that the writer thereof (me) puts herself into a story with romantic intent.
However, I thought it was a fun premise regardless of whether it was a Mary Sue or not.
Later for US4. I have to get back to work now!