This is set in season four after episode 3...

It was all Gaius's fault.

Well, you couldn't entirely blame the old man, he was only a tiny bit interested. A bit like Merlin and the Goblin, he was only interested a tiny bit interested in what was inside the box but out came trouble. Same thing with Gaius and the book. He didn't mean to cause any harm, not at all. What happened... Sadly happened.

It all started on a normal hot summer's day. Around two months had passed since King Uther's death and everyone was still finding it a little bit hard to believe. Thankfully, Arthur had been coping well and was turning out to be a fine King himself.

A group of Druids had been spotted near Camelot and Gaius had been sent to the library to find out how far this group went back. Of course though, Merlin had to help Gaius carry the books. At least it got him out of cleaning the stables.

The pair scanned the shelves, trying to see what book would be useful. This wasn't exactly easy with every book covered in an inch of dust. As ever, the library was silent, every footstep you made could be heard. Merlin stared up at the shelves he was looking at and wondered why they needed so many books on one subject that said all the same things. Having no idea where to begin, he started pulling books out at random and pretended to read. He was here to help Gaius carry what books he needed, not look for the books he needed.

As Merlin wasted his time slowly becoming bored, Gaius was actually trying to find a book on these Druids. If he was correct, they could be the main stream of Druids – the first group to ever form. They'd be more powerful and wise than any other group the knights would have encountered before. However, Gaius was getting old, and so decided to check.

Waddling along the shelves, Gaius spotted a book somewhere it didn't belong. It was uncommon for a book to be in a wrong place. Slowly, Gaius pulled the book off the shelf, dust falling to the floor. He flipped the book the right way round to see the front cover.

"Book of mischief," Gaius read aloud. Ignoring the buckle on the book as a warning, he undid the buckle and opened the book anyway.

Inside the book were many pages on troublesome, mischief-causing creatures and all sorts of mayhem causing spells and potions. Gaius was indeed happy that he had found it before anyone else (mainly Merlin) as they might be tempted to use it. Still flicking through the book, Gaius hadn't noticed Merlin wonder off round a different bookshelf, out of the old man's gaze.

Gaius continued to flick through the book. Despite how bad it was, it was actually quite fascinating. The part on mythical creatures could be quite useful. Suddenly, a closed envelope flew out of the book and landed neatly on the floor. Gaius bent down to pick it up. He recognised the crest on the seal anywhere as Pendragon. Intrigued, he began to open the envelope. Gaius opened the letter, pulled out the paper from inside, and began to read.

"From twisted words that you read,

A Prisoner shall escape,

Do not fear, as none shall bleed,

Nevertheless, he is a pain,

And fears no shame,

In his unholy deeds," Gaius read aloud. Unsure of what the words meant, he began to reread them. Unseen to Gaius, a faint blue mist started to pour out of the envelope. It sneaked along the floor, drifting over and around books left lying around. Floating out of Gaius's line of vision, it crept round a different bookshelf.

Merlin stood innocently, reading a book and humming a sweet melody his mother had taught him from a young age. He placed the book back in the correct place and pulled another one out. After a debate with himself, he decided to actually help Gaius find the book he needed. The blue mist slowly floated upwards and started to circle around Merlin's feet. As Merlin was looking up at the top shelf, he could not see the mist. Not even as it started to swirl up around his body like vines, within seconds reaching his waist. From there, the mist crawled up his back, sending a shiver down his spine. It then lashed over his shoulder and started to force Merlin's mouth open and itself down his throat.

Dropping the book that he was holding, Merlin stumbled backwards, clawing at the mist. However, it was no good. The mist forced itself down his throat, and into the very core of his body, entangling itself with his soul. Merlin's eyes bulged, as if he couldn't breathe and his head snapped back. It was all over in seconds.

Whatever the mist was, it had forced itself inside of Merlin and succeeded.

His head snapped back forward and his eyes glowed red, before turning back to his beautiful blue. Letting out a long sigh, he loosened his limbs just as Gaius came round the corner.

"Merlin, I found this book. I think Uther's great grandfather wrote this letter that I found inside it," he said, showing Merlin the letter and letting him hold the book. Merlin's eyes shone with excitement. He smiled as he read his in prisoner's words. Suddenly clutching the book to his chest he said:

"I'll take this back to your chambers, I just remembered..." Merlin rolled his tongue across his teeth. "I have to help Arthur with... Something," he said, over stating the 'something'. Before Gaius could object, Merlin walked past him at a fast pace and disappeared from the library, the door slamming closed behind him.

Confused with what had happened, suspicion started to blossom inside of Gaius.

What had he just seen?

Merlin hurried down the empty corridor. His head would twitch to the side every so often, to show that he was losing control. Seeing a couple of maids walk round a corner, he dived into a hiding place beneath some stairs. Placing a hand on his throbbing head, he concentrated hard.

"Quit it kid!" he thought in his head harshly.

Get out of my body! came a voice from the back of his mind. Despite the protest, the throbbing stopped along with the head twitching. The man within Merlin smiled.

"Just sit back and enjoy the show kid... I'm gonna rock your life," he said to himself, knowing that Merlin – stranded and caged in the back of his own mind – could hear.

I won't let you get away with this... Someone will notice that I'm not acting myself! Merlin screamed from the back of his mind.

"You don't get it do you?" the man asked Merlin aloud. "I've done this before and this time, I'm here to stay," he said before locking Merlin out.

Setting off, he wondered what trouble he could start with.

What did you all think?

Review please.