Severus Snape had been a very complicated man, not only did he hide his own secrets, he also hid others' as well. During the battle of Hogwarts, as he laid dying in the Shrieking Shack, he didn't think about Voldemort, Harry Potter, or even his beloved Lily. He thought about how everyone had good in them, no matter how small.
Goyle, Crabbe, Lucius Malfoy, Draco, Black, Potter, Weasel, Macmillan…
Then, he thought about the members of the Order of the Phoenix and how they must all have hated him.
Well… Maybe not Regulus Black. Severus thought, He was like myself, pretending to work for the Dark Lord but secretly working for the Order.
Severus thought back to the night that he had found out. It had been a cold, damp, winter night when he had been patrolling on the fourth floor. He was huddled in his Slytherin scarf and cloak, but it was still an icy, frigid atmosphere. However, he had been a man of endurance, if he could withstand his Lily's cold glares and Potter's jests, he most definitely could endure the weather. After all, it was nothing compared to the little broken fragments of his heart.
Suddenly, there were footsteps. Quiet measured footsteps that were as rhythmic as a well oiled machine. Tap tap tap tap. Creeping along slowly, Severus rounded a corner and was about to deduct points when he stopped. It was a snake. Not the majestic, sly snakes of Slytherin, but it had the appearance of an evil, cunning, and very angry snake. It's scales were mottled green and it smelled like rot. It had cloudy yellow eyes that seemed to be terrorizing the pictured on the walls. Before Severus could stop that monster from whatever it was doing at Hogwarts, a cold, clammy hand reached up behind him and clamped around his mouth. Too scared to do anything, Severus stood still, waiting in petrified fear. Fear for himself, fearing that the hand belonged to a dementor, or an inferi, or a zombie, or a ghost, or maybe it was the Dark Lord himself! The list went on and on.
Suddenly, a slightly scared, but definitely human voice said, " I don't do well with snakes." The hand released itself from silencing Severus, and a pair of hands spun him around to face none other than his fourth year housemate, Regulus Black. "We have to take that thing down. I can't be late to the Order's meet-. Oh crap!" He quickly clamped his hands down on his mouth. Staring at Severus in fear. Hopeing that he didn't just tell a junior Death-Eater that he was in the Order.
Realizing that the boy standing in front of him was also trying to stop the Dark Lord greatly relieved Severus. "Regulus, it's fine. I'm also going, now let's take down that thing." Nodding their heads at each other, both boys charged out from their hiding places and started pelting down spells down at the snake. The snake hissed and glared menacingly before lunging forwards and snapping it's large ugly maw at the air where Regulus stood. He dodged out of the way and fired more spells at the green reptile. The snake backed up a bit before unhinging its jaw. Pausing for a moment, it sprayed a thick yellow liquid out of its fangs. The liquid that landed on the walls and floor started smoking and burning holes into the stone. It was only the shield spell that Regulus hastily cast that saved the two Slytherins.
"Regulus, that thing must be a blind basilisk, the yellow acid smells like the basilisk venom from potions and the reason why we aren't petrified must be because it's blind. We have to stop it from attacking the school!" Severus exclaimed.
"Maybe we can trick it into spraying acid on itself." Regulus thought for a moment before taking down the shield spell and running head-on toward the basilisk. Using the snake's head as a pole, he launched himself into the air, landing with a thud on the snake's back. The basilisk swerved its head around and aimed a jet of venom at the boy. Jumping out of the way, he collided with the wall. Looking back, he saw to his satisfaction, that the snake had sprayed venom on itself. The great serpent twisted and coiled in pain before ultimately, letting out one final hiss as it fell to the ground. Dead.
"Whew, thanks Severus."
"No problem, but you're in the Order?" Severus asked incredulously.
"How shall darkness be stopped?" Regulus asked in a slow steady voice.
"The Order shall prevail." Severus replied in the same manner, answering the secret code of the Order. Both boys nodded their heads and took off towards the astronomy tower.
It was a strange thing really, if you think about it. Both boys were 'known' Death Eaters, but their loyalties lay with the Order. Both boys were murdered for their beliefs. Thus, Regulus Black and Severus Snape found themselves exactly twenty-two minutes late for the Order meeting. They were harshly dealt with by Mad-eye Moody.