Severus loved Friday evenings. With the classes over and the whole weekend - usually devoted to his potions research - before him, Severus allowed himself time for leisure, time to relax, time to enjoy the deep pleasure of his secret.

*S*S*

Ever since the night of the infamous werewolf incident when he had found out Potter had somehow become an Animagus, Severus had craved to manage the same. His youthful competitiveness pushed him to get even with his enemy.

It had been hard work to do; Severus was never really gifted in Transfiguration. His attempts to become a shape-shifter had taken more then six years. He had interrupted his learning a few times - but never gave up, mind you! - usually when his potions discoveries reached the state of being "nearly done". These were the times when Severus forgot to eat and to sleep, and also forgot to go to teach his classes for a few times, at the beginning of his teaching career.

Severus never gave up. And his efforts were rewarded. Kind of. He became an Animagus. Sadly, it was more than one year after Potter's death, too late to get even with his rival. Even more dissatisfying was his animal form. Severus felt cheated. All those years of studying and practising and what had he got? A completely useless form. Fate really hated him, he thought bitterly.

A few weeks passed before Severus decided to change his form for the second time. After all, he thought, he had given up so much time to accomplish this, so it felt foolish to throw it away. He prepared a somewhat natural environment for his animal form and tried to forget all about other, much more preferable, animals like hawks, owls or snakes.

He changed.

And found unbelievable pleasure.

A feeling he wanted to feel over and over again. It was like a drug.

Over the following years, Severus gradually worked out this ‘Friday routine'. He didn't have time to indulge in his passion more often than this - with the exception of summers. Over the years, he also discovered a few improvements which added to the experience. Tasty little fish, for example.

*S*S*

Severus kept getting the most unpleasant feeling that he was being followed over the past two weeks. He hated the feeling. The war was over and his enemies should theoretically be dead or imprisoned. In Severus' case, however, that group included so many wizards that he would never feel really safe.

Whenever he had turned around or cast revealing spells, trying to detect the follower, he came up empty. And still, there was the prickling in the back of his neck. His instincts screamed at him about danger. Disturbing.

He couldn't wait to change. To feel the freedom again, the peace, the feeling of power. He was the ruler, strong and unchallenged, in his little kingdom. The feeling of absolute safety.

Severus carefully checked the corridor. Empty. He muttered the password and a quick sequence of unlocking spells, and slipped into his quarters.

He checked the water temperature in the pool and licked his middle finger to try the salinity.  Everything seemed to be perfect. Anticipation built in him and Severus spelled his clothes away hastily and slipped into the water. He changed.

*S*S*

Harry Potter left a pet shop in the middle of Muggle London, a wide smile on his bespectacled face. It was the last weekend before Christmas. The first post-Voldemort Christmas. Life was good.

Harry had felt strange - strange in a good sense - since the demise of Voldemort. His burden had been lifted suddenly. Until then, he hadn't fully realised how heavy a burden had been resting on his shoulders.

Harry felt so light! He felt as if he was on a happy mood drug. The euphoria hadn't lasted only for a couple of hours, though. It had been months and Harry was still feeling high.

Everything he did, just anything, only had consequences for him, instead of the whole world. It was so liberating!

Fail a test? No mortal consequences. Midnight dinners on the Astronomy tower? Much better reason for night-wandering than trying to prevent the Dark Lord from re-appearing. Apparating to London instead of visiting Hogsmeade? The worst that could happen was a detention.

Everything was a joke.

Harry supposed that other people felt much lighter too. Headmistress McGonagall, for example, seemed to be more amused than displeased by Harry's shortcomings or pranks. Yes, he had already pulled a fair few pranks worthy of the Weasley twins but she was still amazingly tolerant. He had turned the walls of the Great Hall pink, tempted Peeves to throw Muggle gummy bears at the students and staff, had spelled the door to the library and to all classrooms shut one night, and had invited a Wizard Rock band to play at dinner a few weeks back.

Not only did McGonagall give him unheard of leeway, she also ordered the other teachers to do the same!

Harry walked through a dark corridor back to his dorm - earlier that night he had decided to go and watch the stars - whistling a melody that had popped into his head, but unable to remember what song it was. He wondered if this was how his father had felt during his Hogwarts years. Joyful. Free.

"Potter!" sharp, cold voice stopped him in his tracks. He grinned. Of course, it was around two in the morning, so where else should Snape be than in the corridors, catching night wanderers?

"Hello, Professor," Harry greeted the Potions Master amicably.

His easy tone didn't sit with Snape well, it appeared. The teacher's eyes narrowed and he hissed, "Don't push it, Potter. The Headmistress might have ordered us to be patient with you and let you re-capture your carefree childhood" - Snape's trademark sneer accompanied this statement - "but it doesn't mean I can't give you a detention."

"No risk, no fun," Harry agreed happily. "I'll pop ‘round to scrub some cauldrons tomorrow night. Is 7 p.m. suitable?"

To Harry's immense pleasure, Snape was caught speechless by that comment. "Good night, then, sir," he smiled and turned to leave.

Snape had to have the last word, though. "You whistle out of tune, Potter!" he shot after him. Good thing he couldn't see Harry's huge smile.

That little night intermezzo gave Harry a new idea of what to do in his free time. He started stalking Snape. The man was a walking challenge! Harry could swear Snape had a sixth sense as far as detecting another person's presence was concerned.

Harry spent nearly all his free time in the library in the following three weeks. He decided not to use his cloak, it felt like cheating. Instead, Harry tried to find and learn every concealing charm and obscuring spell available. He studied how to become unseen, how to mask his smell and the noise of clothes and feet, and all other possible indicators of his presence.

He started following Snape. First during the days, as his presence could be easily explained, in case Snape caught him. Then he started following Snape on his night errands. The ultimate challenge, though, was to sneak to the man's quarters.

Man, was Snape difficult! The ex-spy proved to be the challenge Harry had expected him to be. Snape kept sneaking glances all around. His black eyes were sharp like laser beams. He cast nonverbal detecting spells with a speed of a viper. Harry had grand time avoiding detection.

And then, one night, Harry succeeded.

One nice Friday evening, he made it into Snape's quarters.

The feeling of victory quickly changed to shocked surprise. He followed Snape to a room that was actually one big swimming pool. Wow, Harry thought dazedly. The room was of a size of their dormitory. More shock was yet to come, though. All of sudden, Snape spelled his own clothes away.

Harry gasped. There were many things in his life he wanted to see, but a naked Snape was definitely not among them. Harry stared at the man's white buttocks in horror. If he finds me, I'm dead, he realised.

But Snape didn't find him. He even didn't turn around. He spryly got into the pool and vanished.

Harry blinked. Then he realised Snape had simply dived under and was swimming beneath the surface. The best time to get away from the quarters was now.

Harry was already at the door when he suddenly paused. He couldn't hear Snape surfacing. Surely the man couldn't stay underwater for so long? Harry waited for a minute. Nothing.

What kind of ludicrous accident was this? Snape getting drowned in his own swimming pool with Harry present? Harry quickly went back to the pool's border and peered in. Snape was gone.

Harry blinked and thought furiously. What kind of joke was this? His eyes narrowed. Maybe Snape had known all the time that Harry had been following him? Maybe the Slytherin had turned the joke on its head - at Harry's expense. He should have known! Harry grinned against his will. Snape really got him. Fair enough. Harry looked behind him. No shouting Snapes. Not yet, anyway.

It was a strange pool anyway, Harry observed. It was a replica of a sea shelf - as far as Harry could tell because it was not as if he had ever seen one, as the Dursleys always left him with Mrs. Figg when they left for a holiday. On the bottom, there was sand and some rocks, and also a few sea plants. Little fish swam around a big rock near the side of the pool. It was beautiful.

Harry was thinking hard. Could Snape be a... fish? He taught Potions during the day and he got back to his fish family in the evenings? Harry mulled over the weird idea, staring into the water, fascinated. Suddenly he noticed another occupant of the pool. A big black and white jellyfish. Snape. It had to be.

Snape caught one of the fish and devoured it.

Harry shook his head amusedly. It made sense. Give it to Snape to turn into a beautiful and mortally dangerous animal.

Harry let himself out of Snape's quarters, grinning. He badly wanted to share his discovery with his friends. Or to confront Snape. He knew he couldn't, though. Snape would certainly kill him for such indiscretion. Harry had to keep his knowledge from everyone.

His new mischievous self decided otherwise, however. Hence the pre-Christmas visit to a pet shop.

*S*S*

Severus had already opened his three annual Christmas presents - from Albus, from Minerva and from Draco. Now he was pensively watching the fourth box. He read the label again.

Happy Christmas, Severus! It stated. Anonymously.

Quick sequence of danger-revealing spells later, Severus opened the present carefully. He stared in shock at a tank containing three fish. The same kind of fish Severus kept in his little kingdom.