The Traitor Mortals needed to return to their lands being that nearly every able bodied fighting age male was not farming his lands or doing all of the other work necessary to keep a community functioning. And so eventually they decided to withdrawal from Mortal territory and yet they wanted to protect their rear and so tasked [Saireus] with the job. He had with him the young man Vispereyl as second in command (who he was mentoring at the request of his father). Their job was specifically to keep up an attack to cover the withdrawing army but their task was not meant to be a short term project, on the contrary they were to lead their own long term campaign as it seemed a quick withdrawal might indicate a weakness and thus convince the Mortals that they should attack.
[Saireus] took this new assignment but he wanted to get home to his family and to his lands so that he might have a successful harvest of his crops (and to protect what was his from those who might be anxious to take his property in his absence as none of his sons were old enough to do the job). Even though, [Saireus] did as he was commanded, grudgingly, but for Vispereyl he quickly saw an opportunity to profit immensely from this new assignment. He worked on convincing [Saireus] to consider the riches that could be gained by staying and continuing to raid, even pushing ever deeper into Mortal territory (greatly expanding the purpose of their orders). Although [Saireus] did not want to stay he did put the proposition to the leaders (via messengers) and it was decided by them that it would not be a good idea as it might focus the rage of the Mortals and cause a second war of retribution. (which at this point they were looking to avoid at all costs.)
[Saireus] obeyed, having no real desire stay anyways with all that awaited him back home. Vispereyl on the other hand had very little to return to, no wife, children or property and did not like the idea of returning to his parents empty handed at some point in the near future. He made up his mind that he would not return anytime soon regardless of the orders given and that if [Saireus] returned he would stay on and attempt to implement his plan. All he would need would be a small band of followers who could see the potential before them and would be willing to take the necessary risks.
[Saireus] and Vispereyl disagreed on their next move and once their assignment had been completed (their main forces having withdrawn and a slow draw down completed) they separated, [Saireus] returning home and Vispereyl staying, having recruited men similar to himself who had little to return to with words of possible wealth beyond what they could expect back home. They decided not to turn away from the opportunity presenting itself and therefore to make their fortunes here and now by the sword.
When [Saireus] retuned the leaders of the Siradyt were not happy that Vispereyl had stayed behind and told [Saireus] that he should have brought Vispereyl back. They had made it clear before that any deviation from their carefully considered plan could risk provoking the Mortals into a new war of retribution. They had specifically designed a plan of action for psychological terrorism and Vispereyl’s actions could end up undoing the physical and psychological gains they had just made against the Mortals.
Messengers were sent to Vispereyl with orders to return at once but he refused to return and the messengers returned with the news that pushed (the leaders) further into a corner. Additional messengers were sent with a more adamant demand and as before they returned with bad news (Vispereyl will not comply). At some point the Siradyt leaders felt their only recourse was to assassinate Vispereyl and as many of his men as possible and so a small pack of killers was sent in the guise of messengers to assassinate Vispereyl.
This assignation attempt was a complete disaster and all of the men sent were themselves killed, their heads being returned to the Siradyt leaders as a message from Vispereyl to them that he and his men were now a force to be reckoned with. They were now brigands and the Siradyt leaders could attack them with their army and all the dangers that might bring or cut them loose. As Vispereyl and his men had been effective in becoming the primary focus of the Mortals the Siradyt decided to cut them loose, providing no support, figuring the Mortals would eventually kill them all. (they could even ally with the Mortals against them if that option became viable.) They could use the time to train their own army in case the Mortals killed Vispereyl and his men and continued onward for vengeance.