so you haven'y played bo2 or at least not single player...
ok here is the plot from just mp then
a group of mercenaries has done well, many wars have meant many big contracts, to the winners the spoils. these guys are loaded so they buy a luxury yacht and villa.
one night they go clubbing at a wealthy luxury resort, its their first holiday, which they have earned by risking their lives day in day out in the many oil wars. when the security guards find out they are just mercs they get jeleaous of their wealth and a fight starts. being bad ass mercs they hustle up some gear and lots of people get shot so they decide to leave as it was a holiday they wanted not a fight
on their way home onboard their luxury yacht they think finally. peace at last. but the fbi attack them because the guys at the bureau only pull average salaries so envy strikes again. the bad ass mercs defend their yacht but are left pretty pissed off as they just want to chill out
they get home and decide to go for a skate to chill out only to find that since their holiday those same damn fbi tools have started skating at their skate park. Damn! a fight ensues and many people die.
they decide to catch the train home but again its a bad move as an fbi convention sees more of the green eyed fbi bast*rds at the station who recognise them and their dimond camo guns, many more people die but they get home to their luxury villa unscathed. they are bad ass mercs after all.
they order pizza and chill by the pool, the door bell rings and pete the mercenary goes to answer it, guess who, yep those envious fbi guys are really mad now, a massive fight ensues and many people die.
the mercs are really pissed now and decide to go and escape to a ski lodge, the moutains are quiet and they may finally get some rest, after all they just want to relax but irony strikes again and the lodge has been double booked. turns out the fbi wanted some down time after taking a beating from the mercs.... a massive fight ensue and many people die.
meanwhile some random chineese forces attack a carrier, a military base in yemen and the americans decided to invade some packing crates in hong kong after all, that random crane that just moves the same 4 crates about must be a secret military weapon as it doesn't provide the functionality of a real crane. turns out its a **** crane but many people die to discover this
equally the chineese are very angry when they discover the carrier is a fake as it couldn't function as a carrier and the drone facility is also just a fake as it can't do anything. many people die and everyone leaves confused.
meanwhile a holiday goes wrong in yemen and some randoms in pakistan get very angry when the jobs they were promised in a nuclear facility turn out to be an american tv show hoax, they get guns, the americans already had guns, theya re yanks after all and a big fight happens and many people die.
hope that clears it all up for you