This is set at the end of Series 3, so there are slight spoilers for everything up to that point.
Disclaimer: I don't own Merlin. Now you know what to get me for Christmas!
Morgause held the small pouch lovingly in her hands, caressing it occasionally. She was still injured from the battle for the Cup of Life, but she was slowly regaining her strength. She was ready to put her next plan into action.
"Sister," Morgana's greeting pulled her out of her reverie, "You wished to see me?"
"I did," Morgause smiled and beckoned her sibling over, "Come, sit by me, and see the power that will destroy our enemies and put you back on the path to ruling Camelot."
Morgana's cold eye's lit with anticipation as she knelt by her sister. Morgause raised the leather pouch in her hands and eased it open, giving Morgana a glimpse of the fine powder inside. Green eyes met brown as Morgana's brow wrinkled in confusion. Morgause smirked as she continued, "I too have seen glimpses of the future, and they have shown me Camelot's weaknesses. I have seen knight fighting knight, friend turning on friend because of one thing… jealousy."
"Between who?" Morgana smiled eagerly, "Over what?"
"One of Arthur's knights is not as pure as he would have others think," Morgause said slyly, "Sir Lancelot longs for something he cannot have, something he once had a claim to, something he will never be allowed to possess again."
Realization dawned in Morgana's eyes, "Gwen!"
Morgause nodded. "All it would take is a small push, a gentle nudge, and he would let go of his restraint and try to win Guinevere back."
"Arthur would never allow it," Morgana wanted to laugh with joy, the plan was so simple, so brilliant, "They would quarrel, and some knights are bound to take Lancelot's side. Their so-called round table would split in two!"
"They will do more than quarrel," said Morgause, "They will tear each other to pieces, and they will do the same to anyone who tries to get between them." She raised her pouch. "This dust is extremely rare, valuable, and magical. If the incantation is said and more than one person breathes it in, whatever they share love for will become the object of intense jealousy. It could be a possession, a place, a pet, a friend, a family member…"
"Or a woman," Morgana finished.
"Yes," a wicked gleam came to Morgause's eye, "And the more powerful the feeling, the more powerful the enchantment. They will become possessive, feel angry and envious if Gwen spends time or speaks with anyone else. They will have no remorse, no empathy. They will not care what Gwen wants— they will see only their own desires. Even the one she chooses to be with will have no peace. He will always be on guard and suspicious. Is she thinking about the other? Is she going to change her mind and leave? Their love will be twisted into an untamable monster. In the end, the two will see no choice but to kill each other. They will tear themselves apart, along with Gwen and anyone who stands between them."
Morgana's eyes shone with excitement and determination as she took the pouch and met her sister's eyes.
"What must I do?"