There are four primary groups that will be entering site-19, all of them made up of other fictional characters from other universes (yes, I’m a sucker for big crossover battles, bite me). Group A is composed primarily of villains and other ne’er do wells, and they and their mysterious, evil “master” are the ones responsible for wrecking site-19 in the first place. Their mission is to round up and weaponize as many dangerous SCPs as possible and smuggle them out of the universe. Group B and C are in direct competition with one another- both of them have arrived in the SCP-verse in order to recover another SCP, one that’s actually a component of an ancient super-weapon. (I was thinking of 399 here, but if this ticks off the original author I’ll just change it to some generic SCP) Group D has arrived by accident, and between trying to dodge the in-fights of B and C, the machinations of A, and getting chased by monsters and such, are trying to restore power to the base and escape intact. Therefore, each of them will have separate goals and different routes through the chaos, but this is for the most part a rough outline.
Groups B and C arrive simultaneously in the D-class barracks. Although they initially try to keep a low profile in order to retrieve the SCP without the other knowing, group A shows up not long afterwards and engages them in battle. In their initial attack, the power systems are knocked out, the phone lines are cut, and every door is blown open through supernatural force- fortunately for the rest of the planet, the site is placed into lockdown before anything can get outside. Among the chaos, the groups are split up from one another.
Group B breaks into the office of one of the site directors to find the SCP they’re looking for. Although they manage to discover the location and abilities of the relevant artefact, they are attacked by SCP-106, who wrecks up the place a little bit, eventually chasing them through the office facilities and into a storage locker system for Safe-class items. Naturally, the group can use some of these things to creatively fight off 106 or aid their escape; after this point, they force their way out into the main containment chambers and begin looking for the SCP.
Group C, on the other hand, winds up taking the elevator down into the lower levels of the site, where the majority of Keter-class objects are stored. However, as they do so the elevator is stopped and choked by SCP-1100 running rampant, forcing the group to fight their way down the elevator shaft into the sub-basements- little do they know, however, that SCP-457, with the sprinkler system offline, is attempting to burn his way up through the ventilation system and reach the top level of the facility. As they attempt to escape/fight/temporarily extinguish the burning man, they accidentally stumble across the remains of a tank of acid. Its owner has only just regenerated his legs and is extremely cranky…
Amid the chaos, Group D arrives at the topmost level of the site; although naturally it’s abandoned save for SCP-847 and SCP-250. Upon their arrival, 847 attempts to chase down the various females of the group, while 250 goes after everyone else (including 847!) After killing/trapping them, however, they manage to encounter Group B. In addition, they happen upon Mr. Deeds, who provides them with more information about the Foundation and what the optimal course of action should be- he believes that the most effective way to bring about order to the Foundation is to attempt to restore power, round up the escaped Keter and Euclid-class SCPs or terminating them should no other option present itself. Accordingly, he guides them down to the basement generators; unfortunately for the group, several samples of SCP-363 have already decided to make the dark basement their new home and have begun laying eggs in some of the more unfortunate D-class personnel. Mr. Deeds is “killed” in the battle, but Group C, now trying to outrun both 457 and a very pissed off, asbestos-lined 682, accidentally happen upon D during the chase, burning 363 alive. After escaping from 682 again, the two groups form an uneasy truce as they try to first restore power to the facility and then find a way out of the basement-the elevators are out of commission.
Group B finds itself in another wing of the Foundation, still searching for the SCP. As they do so, however, they come across a loose group of researchers, agents, MTF members, and D-class, guarding some of the Safe-class SCPs in a temporary panic room. As Group B and the researchers try to formulate a plan, however, the villainous members of A, now with several items in tow, slaughter the researchers and make to attack B; but at that moment there’s the sound of concrete and rebar scraping across the floor, a sudden snap and a gurgled scream from an inattentive researcher… and I think you can guess who’s showed up. =p
Fortunately for the heroes of Group B, the lights come up in time (thanks to groups C and D in the basement) for them to locate and escape from 173, which pursues them as best it can (depending on whether or not the group is aware of its properties). As they try to escape the statue, Group A makes off in the other direction, stumbling across the macguffin SCP in the process. Realizing what it is, they immediately make off with it, trying to get to the entrance even though it’s still barricaded shut. However, with the power systems online, the auto-failsafe mechanisms come into play; the onsite nuclear bombs will arm themselves and detonate in two hours unless the 05 council is contacted. The group will either need to find an SCP that will allow them to escape to the outside world or find a way to jury-rig a phone line from within.
In the basement, Mr. Deeds and the rest of the group manage to temporarily trap or kill several rogue SCPs before finding the emergency stairs, with 682 still in hot pursuit, shrugging off their attacks and growing stronger and angrier by the minute. As the two groups move upwards, they come across something strange even by the Foundation’s standards- a glowing humanoid creature moving in the other direction, slick with blood and appearing strangely frightened. His appearance is consistent with the other space-gods that they have encountered; when he is interrogated, he maintains that at present he must remain in the Foundation universe and allow himself to be taken into custody- to “protect the multiverse from himself”, he claims, refusing to elaborate. (This is foreshadowing for non-SCP-verse stuff, so don’t worry if it doesn’t make sense). However, even as 682 spots them and closes in for the kill, their benefactor teleports them to the top level of the site before drawing 682’s attention and leading him on a chase to distract him. With all four groups now converging, Group B and C recognize the stolen SCP that they must recover, facing off against each other and Group A for control of it. However, even as they lose control of the important SCP, A manages to escape through a portal with several other SCPs in tow, for purposes unknown. B and C also escape through portals, leaving only D in the site that is rapidly going critical. As soon as they manage to contact the O5’s, however, they are swept up by an unknown force and deposited in places unknown…
…so, how was that? Did it rape canon too much, or does it seem pretty enjoyable? Granted, I had to fudge a couple of things in order to make sure that everyone doesn't get massacered alive within five minutes, but otherwise…
