Edward and Thomas's relationship hit a low point in the summer of 1316: the two men met and had a furious row in York, and although Thomas was chosen as one of the godfathers of Edward and Isabella of France's second son John of Eltham, Thomas's great-nephew, he failed to attend the boy's christening, a gross insult to the king and queen. (I can't help wondering if Edward - criticised then and now for his closeness to his male favourites - felt a tad smug that he had fathered two legitimate sons while Thomas, in his late thirties in 1316 and a man who supposedly "defouled a great multitude of women," had none?) The author of the Flores Historiarum, whom I always think of as Not Edward II's Greatest Fan, claims that Edward armed himself against his cousin and that his fear of Thomas was the reason for his cancellation of the Scottish campaign that was meant to take place that summer.  Whether that's true or not, Edward was concerned enough about Thomas's hostility to summon Isabella to him in York after John of Eltham's birth, fearing for her safety. The queen travelled very fast: on 22 September 1316 she was at Buntingford in Hertfordshire, 175 miles from York, and must have been reunited with Edward soon after the 27th, as on that date, the king paid her messenger William Galayn a pound for informing him of her imminent arrival. 
In the spring of 1317 came the abduction - or whatever it was - of Thomas of Lancaster's wife Alice de Lacy from Canford in Dorset by household knights of John de Warenne, earl of Surrey. Rightly or wrongly, Thomas blamed Edward II and the three knights then high in the king's favour, Roger Damory, Hugh Audley and William Montacute. Whatever the truth of Thomas's allegations, it seems clear that Damory, Audley and Montacute were doing their best to hinder any reconciliation between the king and the earl, and at a meeting of the king's council at Clarendon in the spring of 1317, the three openly called Thomas a traitor.  Thomas sent letters to Edward to say that "he fears the deadly stratagems of certain persons who thrive under the protection of the royal court…they have already carried off the earl’s wife to his disgrace and shame."  Thomas asked Edward to expel the earl of Surrey, Damory, Audley and Montacute from court, and demanded "such satisfaction as he can get for the wrong done to him." He wrote to Edward to complain that his companions were "not suitable to stay beside you or in your service…but you have held them dearer than they ever were before...every day you give them of your substance, so that little or nothing remains to you."  To be fair, he did have a point: Damory, Audley and Montacute had no intention of allowing Lancaster to reduce their vast influence over Edward and therefore counselled the king to remain hostile to his cousin and "intrigued against the earl as best they could." The Flores calls them "men who stir up discord and many problems for the kingdom daily attending the lord king, continually supporting his arrogance and lawless designs."  Pope John XXII tried to heal the breach between the king and his cousin in 1317 and 1318, begging Edward not to allow any "backbiter or malicious flatterer" to bring about disunity between himself and Thomas, and to send away from court those men who offended the earl. The pope also asked Thomas to "separate himself" from those who displeased Edward and to reject "suggestions of whisperers and double-tongued men." 
Edward and Isabella left Nottingham and the failed council meeting on 7 August 1317, and travelled to York. The king was forced to stay as far to the east of Pontefract, Thomas's stronghold, as possible: the most direct route would have taken him right through the town, but Thomas had blocked his way by placing armed guards on the roads and bridges south of York.  Edward was, understandably, furious that one of his subjects would dare to impede his progress through his own kingdom, and brought it up four and a half years later as one of the charges against Thomas at his trial.  Before Edward’s arrival in York, he did, however, send envoys to Pontefract to negotiate with Thomas, to try to make peace so that the latest planned Scottish campaign could proceed. The envoys included the archbishops of Canterbury and Dublin, five bishops, and the earls of Pembroke and Hereford, their aim to persuade the king and the earl to meet face-to-face and resolve their difficulties; "a love-day without the clash of arms," as the Vita puts it. Unfortunately, Thomas claimed to have heard a rumour that if he came to Edward’s presence, the king would "either have his head or consign him to prison," and, whether that was true or not, refused to meet Edward. Thomas also accused Roger Damory and William Montacute of trying to kill him, and claimed to have intercepted letters from Edward II to Scotland, inviting the Scots to help kill him. 
Fortunately, however, at the instigation of two cardinals who had recently arrived in the country – they were with the king at York in September 1318 – a date was finally set for a meeting between Edward and Thomas, although it was postponed. For now, at least, Edward agreed to take no hostile action against Thomas and his adherents, and Thomas agreed to attend the next parliament, due to be held at Lincoln in January 1318. On 26 September 1317, Edward granted a safe-conduct for "our dear and faithful cousin" Thomas, and his adherents, to travel to Lincoln the following January.  Finally, Edward dismissed most of his soldiers, Thomas removed his guards from the roads and bridges south of York, and at the beginning of October 1317, Edward left York to return to London. The road through Pontefract was now clear, but instead of doing the sensible thing and ignoring Thomas, Edward took it into his head, despite his promise a few days earlier not to take action against his cousin, to command his men to take up arms and attack him. Apparently one of Edward’s friends – most likely Roger Damory – had persuaded him, in his own selfish interests, that the earl posed a threat to Edward and that he should attack him first. Fortunately for the stability of his kingdom, Edward, who was incapable of distinguishing between good and bad advice and who tended to believe and act on whatever the last person had told him, informed the earl of Pembroke beforehand what he was intending to do. He said "I have been told that the earl of Lancaster is lying in ambush, and is diligently preparing to catch us all by surprise."  Pembroke fortunately still retained some influence over the king and managed to convince Edward that this was not in fact the case, and the party returned to London with no further incidents – despite the fact that Thomas did his utmost to make matters worse by leading his men out to the top of the castle ditch and jeering at Edward as he and his retinue travelled past.  Edward was naturally incensed at this appalling rudeness, and he was not the kind of man to forgive and forget an insult; in March 1322, it was another of the charges he raised against Thomas at his trial.In early October 1317, Thomas seized Knaresborough Castle in Yorkshire, which his retainer John Lilburn didn’t surrender to the king until January 1318, and by the beginning of November had also forcibly gained possession of Alton Castle in Staffordshire. Knaresborough had formerly belonged to Piers Gaveston, Alton to Theobald Verdon, but far more importantly as far Thomas was concerned, Roger Damory was the custodian of both. Edward ineffectually sent out orders to various sheriffs to retake the castles and commanded Thomas to "desist completely from these proceedings." Not only did Thomas fail to obey, he "with a multitude of armed men, besieged and captured diverse castles" in Yorkshire which belonged to the earl of Surrey: Sandal, Conisborough and Wakefield. Thomas also ejected Maud Nerford, Surrey's mistress, from her property in Wakefield, and by the beginning of 1318 had taken firm control over Surrey's Yorkshire lands.  In an attempt to placate his cousin and persuade him to give the castles back, Edward told him "the king is prepared to do justice in his court concerning the things that the earl has to prosecute" against Edward’s friends, and paid Alexander Bicknor, the English archbishop of Dublin, forty pounds for travelling to Pontefract to talk to Lancaster.  The conflict between Surrey and Thomas continued unabated in 1318: Thomas now turned his attention to Surrey’s lands in Shropshire and Wales, and Edward issued an order forbidding "his attempting anything in breach of the king’s peace." In July 1318, Edward summoned a meeting of his great council at Northampton, and he and Isabella left Woodstock to travel there on 27 June, only nine days after she had given birth to their daughter, Eleanor. Thomas of Lancaster did not attend the meeting, and the Vita says that the earl of Surrey, Roger Damory, Hugh Audley, William Montacute and both Hugh Despensers arrived at Northampton "in great strength, so that you would have thought they had not come to parliament, but to battle." The author gives this as the reason for Thomas's non-attendance, as "he counted all the aforenamed as his deadly enemies." 
Since April 1318, a group of barons and prelates had been negotiating with the earl of Lancaster, and trying to persuade Edward and his cousin to overcome their hostility to each other. On 8 June, they came to a preliminary agreement: Edward would uphold the hated Ordinances, govern by the counsel of his magnates, and conciliate Thomas, who was threatened with sanctions if he continued to hold armed assemblies. Thomas's violence and lawlessness were thus condoned, as he was too powerful for the king to ignore and his co-operation with Edward was essential if England was ever to find peace. Although Thomas declared that he did not trust Edward’s safe-conducts, he did eventually consent to meet the king, and on 7 August 1318 the two men exchanged the kiss of peace in a field between Loughborough and Leicester. Edward gave his cousin a fine palfrey "in recognition of his great love" of Thomas. (Hmmmm.) A formal agreement, the Treaty of Leake, was signed in the town of Leake near Loughborough two days later. 
So by late 1318, the relationship between Edward II and the earl of Lancaster was about as good as anyone could have hoped for, and in September 1319 Thomas actually co-operated with the king and took part in the siege of Berwick. But the actions of Edward's latest and most powerful favourite were soon to cause the relationship to deteriorate once more, and this time, it would result in execution...Coming soon!
1) Flores Historiarum, vol. III, ed H. T. Riley, pp. 176-177.
2) Calendar of Patent Rolls 1313-1317, p. 621; Thomas Stapleton, 'A Brief Summary of the Wardrobe Accounts of the tenth, eleventh, and fourteenth years of King Edward the Second', Archaeologia, 26 (1836), p. 320.
3) Flores, p. 178; J.R.S. Phillips, Aymer de Valence, earl of Pembroke 1307-1324: Baronial Politics in the Reign of Edward II, p. 119.
4) Vita Edwardi Secundi, ed. N. Denholm-Young, p. 80.
5) G.O. Sayles, The Functions of the Medieval Parliament, pp. 336-337.
6) Vita, p. 87; Flores, pp. 176-177.
7) Calendar of Papal Letters 1305-1341, pp. 415, 431, 434, 438-439, 444.
8) Vita, pp. 80-81.
9) Phillips, Valence, pp. 119-120.
10) Calendar of Close Rolls 1313-1318, p. 482; Foedera 1307-1327, p. 335.
11) Gesta Edwardi de Carnarvon Auctore Canonico Bridlingtoniensi, in W. Stubbs, ed., Chronicles of the Reigns of Edward I and Edward II, vol. 2, pp. 50-52; Adae Murimuth Continuatio Chronicarum, ed. E. M. Thompson, pp. 271-276.
12) Phillips, Valence, p. 125.
13) Foedera 1307-1327, p. 479.
14) Vita, p. 81; Phillips, Valence, p. 131; J.R. Maddicott, Thomas of Lancaster 1307-1322: A Study in the Reign of Edward II, p. 224.
15) Foedera 1307-1327, p. 343.
16) Vita, pp. 81-82.
17) Flores, pp. 180-181; Maddicott, Lancaster, p. 210.
18) Calendar of Fine Rolls 1307-1319, pp. 346-347; Foedera 1307-1327, pp. 345-346; Close Rolls 1313-1318, p. 575.
19) Close Rolls 1313-1318, p. 575; Stapleton, 'Brief Summary', p. 332.
20) Vita, p. 87.
21) Foedera 1307-1327, p. 370; Close Rolls 1318-1323, pp.112-114; Maddicott, Lancaster, pp. 213-229; Phillips, Valence, pp. 136-177; R.M. Haines, King Edward II, pp. 109-117.
(I have no idea why Blogger has decided to put random spaces in my notes. Stupid thing.)