This is what I think happened leading up to Jon's final chapter.
The Wall is yours, Lord Snow
The Wall is yours, Lord Bowen.
The former line is what Donal Noye tells Jon, and Jon later becomes LC. I think the latter line Jon gives to Bowen foreshadows Bowen becoming the 999th LC.
That was quick.
"Please sit," he [Jon] said. "May I offer you food or drink?"
"We broke our fast in the commons," Marsh said.
Interesting that Marsh refuses to break bread or eat with Jon, this can be an early sign of him separating himself from Jon. Jon himself thought that how Marsh and Co, recieved the news of Val was quick. My guess is that Mully is spying on Jon, and reporting to Bowen as Mully is a steward, he was present when Jon sent Val off and finally in Jon's last POV, Mully states that Ghost tried to take a bite out of him akin to Grey Wind receiving the Freys and Rolph Spicer with hostility.
Bowen Marsh did not appear surprised."You mean to let him pass." His voice suggested he had known all along.
This passage reveals that Bowen had known Jon's plan all along, and he has been thinking, and likely planning about what to do regarding Jon's actions. Marsh has been said to be good at counting things so he can be calculating. Also, if we are to draw a parallel to Jon and Julius Caesar, Caesar's assassination wasn't spontaneous but a planned action. I think Marsh had been planning Jon's assassination for quite some time after he knew what Jon was going to do, and couldn't be swayed.
I was eating bean-and-bacon soup whilst Bowen Marsh was going on about the high ground. The Old Pomegranate thought I was spying on him and announced that he would not suffer murderers listening to their councils.
Marsh managed to think that Rattleshirt (Mance) was spying on him, in that case the question is, who does Bowen think Mance would be spying for? Also why would he be concerned with people listening in on his conversations with his group if it is just about things like the high ground, which sounds innocent enough? Marsh and Co were likely plotting, and discussing plans for what would happen in Jon's last chapter.
Bowen had Wick Whittlestick, Left Hand Lew and Alf of Runnymudd.
Alf of Runnymudd was hinted at having a relationship with Garth akin to Renly and Loras given his reaction upon hearing Garth's death. Bowen likely had been picking up allies, and Alf may have placed some of the blame for Garth's death on Jon for sending him out ranging.
When Jon said he was going to meet the Boltons in battle, that is when Marsh and Co. knew they had act fast, and Wun Wun killing Ser Partek was the opportunity for Marsh to put the plan into gear. Marsh had one of his men dispatched to Queen Selyse saying that the wildlings had betrayed the pact made with Jon, and were attacking. I imagine it would be something to the tune of "the treachery of wildlings is well-known". The screams Jon heard behind him were Queen's men present so as to avoid giving any contradictory stories to Selyse and Axell Florent.
When the queen's men come to investigate the first thing they will see is Wun Wun with Ser Partek's mutilated corpse, and they will next see wildlings fighting members of the NW (Marsh and Co.) with Jon lying on the ground, apparently dead with a few queen's men. The queen's men will immediately believe the story given them, and might launch an attack on the wildlings already in the Shieldhall with the black brothers not present at the Wun Wun incident. Marsh will have Selyse name him LC of the NW, and letters will likely be sent out asking for people to aid the NW against wildlings on the south side of the Wall. His plan is to get rid of Jon, and then get rid of the wildlings on his side of the Wall and seal the gates while he's at it.
Edited by Fire Eater, 18 October 2013 - 11:55 AM.