This takes place after some time after 5x08. Morgana's enchantment on Gwen was lifted. It's a one-shot, I won't continue it. Enjoy =)

I don't own Merlin

In her bed, with Arthur's arms around her, Gwen couldn't sleep.

Her mind was a mess: after she was released from whatever magic Morgana had used on her, she just didn't know what to feel anymore.

Guilt, crushing, unbearable guilt for the terrible things she had done.

Relief that she was in her right mind again.

Horror at what could have happened, had nearly happened.

Anger against Morgana for doing that to her.

Hurt and disbelief that someone she had been so close to would even consider doing something like that.

And… doubt.

She doubted herself, more than before. It was the second time she had betrayed Arthur, and even if she knew it wasn't her fault, she couldn't help but fear that it wouldn't be the last.

And somehow, she also doubted Merlin.

Oh, she was grateful he had noticed her betrayal; she had a feeling things would have been so much worse if he hadn't.

But she could remember everything she had done while enchanted, and she knew she had done an excellent job at hiding her treachery; yet Merlin had known almost immediately something was off. Even before she poisoned Arthur, he was already suspicious, she was sure of it.

Her mind screamed that of course he would notice. He was her best friend, he knew her and could tell when she wasn't in her right mind. It wasn't anything to worry about, really.

But her husband, the man she loved with all her heart and who loved her just as much, had remained oblivious. Nor he, nor any of the knights, of her friends, had seen anything. Only Merlin.

Why?

Shifting a little, she smiled when Arthur tightened his grip on her, as if she was something he couldn't bear to be separated from. It warmed her heart that, after everything, he still cared about her.

Her smile faded when she recalled her previous train of thought. She had always believed that Arthur didn't spot the liars and the traitors around him, because he was too honest himself.

And maybe, just maybe, Merlin was the opposite, a little voice in her head whispered. Maybe he could see the signs of deception on people he trusted, because he himself was used to lying.

It takes one to know one, the little voice repeated, over and over again.

Did it take a liar to know a liar?

It wasn't the first time, either: Merlin had been suspicious of Agravaine months before his real allegiances had been revealed. What had he seen that no one else had?

Her mind travelled even further back, when Morgana first took Camelot, with Morgause and an army of immortal soldiers. Merlin had hardly seemed shocked by her betrayal. Had he known about her too?

Could Merlin be hiding something? Merlin, her best friend, Arthur's best friend, who was brave, selfless, and always ready to help someone who needed it?

Merlin, who would tell extravagant stories to explain his last bizarre action, or disappear for hours or days? Who always seemed to know what was happening when no one else had a clue? Who everyone believed to be an idiot when she was absolutely sure he had the sharpest mind of them all?

No, no, it couldn't be. Merlin wasn't able to keep secrets; Arthur complained quite often about this particular trait of his manservant. Or maybe that was an act too?

No matter what she did, that tiny seed of doubt was planted, and even as she drifted off to sleep, her mind was still stuck on that one sentence.

It takes one to know one.