We are introduced to the Rhavin, Graendal, Lanfear and Sammael alliance. Their plan was to aim Rand at Sammael in Illian and for them all to be there when he came.

"He will concentrate on you," the big man [Rahvin] said in a deep voice. "If need be one close to him will die, plainly at your order. He will come for you. And while he is fixed on you alone the three of us linked will take him."

tFoH: Silver Arrow

That "one close to him" is Mat, who is attacked by Melindhra, a DF Aiel and his lover.

"He can keep his honour and take it to Caemlyn or the Pit of Doom for all i care. Don't you worry. I'll find plenty of honour. I will write to you about it. From Tear." He would never escape Rand or Aes Sedai if he made that choice.

"He is going to Caemlyn?"

tFoH: News Comes to Cairhein

From Mat's words Melindhra focuses on Rand going to Caemlyn and believe that this is the reason she waits till that moment before attempting to kill him. She had after all been seeing Mat since the Waste, but when she realises that Rand isn't going for Sammael that he's going for Rahvin instead she knows she has to strike to keep Rand aimed at Sammael. She tries to kill him with a dagger with Sammael's pseudonym's coat of arms upon it.

The dagger. Gold bees in jade. The sign of Illian. Where Sammael ruled.

tFoH: News Comes to Cairhein

It all went perfectly until Mat brought word of Morgase's supposed death at the hands of Gaebril (Rahvin) in Andor. So instead of going to Illian to where a trap awaits him, he goes to Caemlyn and kills Rahvin. Which now leaves only Graendal and Sammael in the alliance.

Before that i think that Graendal, Asmodean and Lanfear has their own alliance.

In passing Asmodean speaks of being in Arad Doman.

"I came across a saying in Arad Doman 'The more women there are about, a softer a wise man steps'"

He later goes on to say

"Graendal was in Arad Doman for a time"

tFoH: Pale Shadows

I believe that Asmodean was with Graendal in Arad Doman, their personalities i think are quite similar. Both are self-indulgent and fond of excess, we often see Asmodean dressed exceedingly well and enjoys his wine and lounging while playing his harp. I can see them getting on well.

So Lanfear goes to visit Graendal in Arad Doman to create the alliance we see in tFoH. When there she sees Asmodean and an opportunity to persuade him to become Rand's tutor, which is successful. Lanfear knows of Graendal's masquerade as she knows of Sammael's and Rahvin's, it is her that gets them altogether so it's logical to assume this.

"Since you avoid the rest of us, a few of the Chosen will be coming here. I came to you first so you would know it was not an attack."

tFoH: The First Sparks Fall

It's obvious that Lanfear is the orchestrator in this alliance, it is she who found them all and got them all together so she must have known where they all were. I believe she did it to pick them off. She would get Rand to attack Sammael and betray him and Rahvin both, while she and Graendal stood aside. Of course she slipped when she exposed herself at the docks of Cairhien and was killed. But that is of course conjecture.

RJ said that it would be possibly to conclude from only tFoH who's Asmodean's killer was. It was surely Graendal. She knows that Asmodean is Rand's tutor and is following him.

"Are you certain Asmodean went over?" Sammael demanded.

tFoH: The First Sparks Fall

Sammael asks of Lanfear before Lanfear announces it to the group, which leads me to believe that Lanfear told him and Graendal when she was organising this meeting, probably as a spur to highlight how dangerous Rand was becoming, with a Chosen as a teacher.

This would be worrying for Graendal, to have her former ally or at least someone that knew of her hiding place to now be on Rand's side, his confidant. Her motive is to silence Asmodean.

Why does she wait? Because Graendal is a patient and cunning plotter, she doesn't rush in. Plus why bother when she has the tenuous might of three other Chosen on her side. But Rahvin and Lanfear are dead and if Asmodean spills she might be next. So now that half her allies are dead the moment dictates that she strikes. She knows that they are at Caemlyn, so she goes to Caemlyn stalks through the palace hoping to find Asmodean and kill him.

He pulled opened a small door, intending to find his way to the pantry. There should be some decent wine. One step, and he stopped, the blood draining from his face. "You? No!" The word still hung in the air when death took him.

tFoH: Glowing Embers