Commandery after commandery had fallen to An Lushan's inexorable march west, among them Shan (陝郡), Hongnong (弘農郡), Jinan (濟南郡), Puyang (濮陽郡), and Yunzhong (雲中). Alongside Luoyang, all had been captured in the twelfth month of Tianbao year 14 (755–756) alone. Gao Xianzhi and Feng Changqing steadfastly defend Tong Pass, desperately awaiting an opportunity to counter-attack, waiting for a sign of hope.
That hope arrives in the form of a gift box from Changshan Commandery, inside which laid only a plain, wax ball, but the sight of it instantly shocks the commanders. Xianzhi recognizes it as a method of secret correspondence that should be known only to those men who had served under him when he was jiedushi of Anxi. On his order, it was broken to unveil a small scroll within.
An old friend
The letter is addressed to General Gao Xianzhi and all those who should be present at its opening, but it is not for the eyes of those otherwise. Its author introduces himself as a former soldier of the Anxi Protectorate 7th Army 15th Squad, Li E. As the letter is read out loud by Xianzhi, the scene flashes back to Yan Jiming penning it under Li E's instructions. Li E mentions the disaster four years prior at the Battle of Talas, where all his comrades perished and he was the only survivor. Praising the camaraderie and valour of their forces, he consolingly remarks that it was their one and only bitter defeat, one that he should be too traumatized to recall but would nonetheless do so as an old friend.
Though fortune favoured his life, he reports that he was unable to return to his unit immediately, reassuring Xianzhi that it was not for reasons of defection or capture. He tells it truthfully when he recounts that he had resolved to make a last stand on that field of battle, fighting to the end and dying with his brutally slain yet fearless peers. But just as fate seemed to embrace him, he was rescued by the good samaritans of the Western Regions, and because the road back was blocked by Abbasid forces, they withdrew into the desert. Now in the present day, Li E is informing Xianzhi that he is situated at Changshan to assist the family of Grand Protector Yan Gaoqing for one critical objective: to plot a counter-rebellion.
To turn the tide at Tumen Pass
The scene flashes to the point when Li E proposes his plan to Gaoqing, opening with the idiom "capturing the bandit before capturing the king". By his analysis, they "need only to assassinate the two occupying generals, Gao Miao and Li Qincou, and Tumen Pass would then be as a flight of dragons without a chief". He believes that Gaoqing can seize Tumen Pass before the elite enemy marksmen arrive to reinforce it. Once in that strategic position, they would be able to transmit the call-to-arms all throughout Hebei with the announcement that the grand imperial army is already advancing throughout Hebei from Tumen Pass. With this hope rekindled, the people would certainly muster the courage to offer themselves to the counter-rebellion, and the government would be able to march into Hebei unimpeded.
With An Lushan trapped in Luoyang between hostile forces in Tong Pass and Tumen Pass, they would be able to close in on him on two flanks and capture him like a "soft-shell turtle in an urn". Li E closes by repeating again that they only had to assassinate Gao Miao and Li Qincou, and the tide would be turned and Lushan's forces annihilated. Despite his confidence, Gaoqing is pessimistic, musing that it sounded easy on paper yet would prove challenging given the extensive defences of the enemy garrison at Tumen Pass. Li E's determination remains unshaken as he responds, "It would not really be an easy affair; it would also not really be impossible."
Returning to the present, Xianzhi reads that Gaoqing worries that it would be difficult to inspire his trust in the message given that they live in times where one struggles to distinguish friend from foe. For this reason, Li E formally requests by his old position as his subordinate that the general dispatch troops to Taiyuan and await a rendezvous.
At this, Xianzhi finally pauses to inquire Changqing about this Li E. As chance would have it, his lieutenant had memorized the names of the soldiers who had served with them at the Anxi Protectorate although his mnemonic required that he list them off in a certain order to recall them. Counting down with his fingers to Li E's purported unit, then down the ranks and the squad members, he finally arrives at Li E on the eleventh name to his own surprise. Changqing explains that there truly was a soldier named Li E who had fought for them and that he was part of a squad of elite crossbowmen, a squad which was destroyed at the Battle of Talas.
The letter does not end there. Li E reveals that the forces of Changshan are departing the very night of the time of the letter's writing. In another flashback, the Changshan militia have gathered before Gaoqing as he announces their strategem to them. Among their ranks are Li E, Yan Jiming, and He Hong'er. According to the plan devised by Gaoqing, they will present an abundance of fine wine and exquisite delicacies to the Yeluohe garrison at Tumen Pass under the guise of hosting a gracious feast. Once the enemy troops have gotten drunk, their warriors will grab their weapons and slay them all. Meanwhile, their other troops will be hiding in ambush outside the pass, waiting for Gaoqing's signal to strike, which he will give when he has rooted out all the enemy officers and close followers. They will then collapse on them and kill the rest of the garrison.
They march off in the dead of night with their transports of food and wine. As they do so, the scene slowly fades once more back to the present as Xianzhi reads the final words of the letter. Li E humbly admits that as a commoner of low station, his formal education has been shallow and his literary ability inadequate. Therefore, he had the secret message ghostwritten by his good friend Yan Jiming, the son of Grand Protector Yan Gaoqing. Rather than detracting from its sincerity, however, Li E asserts that in this light, the letter carries not just the will of his heart and his heart alone but that of the Yan family as well. By extension, it also reflects the heart of the myriad people of Changshan. He wishes that through their counter-rebellion, they have brought a slimmer of hope to General Xianzhi, and he wishes that General Xianzhi will also become a hope to Changshan.
These touching last words bring tears streaming down not just Xianzhi's face but those of all the officers standing around him. Now knowing that they have not been abandoned and with a gateway to salvation before them, the entire room cannot help but vent their pent-up anxieties until they are at last interrupted by one of these officers. He shouts that Xianzhi is too vital for the defence of Tong Pass to leave under any circumstances while those elite troops under Changqing are too exceptional to spare. With a booming voice and his hands clasped together in respect, he pledges himself as the commander of the Feathered Forest of the Right that he would dedicate his utmost strength to bring the mission to fruition.
Having recovered his composure, Xianzhi gazes for a moment past the commander at an eagle soaring in the sky outside before at last offering his blessings and instructing him to fly the banners and march off to victory.