Apotheosis of career
In the years after James I's return to Scotland, the king's relationship with Alexander of Islay, Lord of the Isles, began to decline. Alexander offered his support to the king when the latter arrested the Lord of the Isles and his mother, Mariota, Countess of Ross, in 1428. Open warfare erupted between James I and the lord's Clan Donald kinsmen the following year. Alexander and his affinity participated in the king's campaign against the Lord of the Isles and his family, which culminated in the Battle of Lochaber on 23 June 1429. Alexander's support of James I in 1429 allowed him to recover the preeminent position he had held under the Dukes of Albany. The king returned practical control of northeastern Scotland to Alexander, under the customary title of "lieutenant". Alexander was additionally rewarded in 1430 with the king's grant of Lochaber, which had previously been held by Alasdair Carrach, one of his enemies at Harlaw. Although James I viewed his cousin as a dependable royal official, Alexander himself likely accepted the king's support with the aim of increasing his own local power.
With his authority in northeastern Scotland strengthened, Alexander took a leading role in royal campaigns against Clan Donald and Clan Mackay. Alexander worked actively to weaken the Lordship of the Isles by arranging the marriage of his daughter, Janet, to Lachlan MacLean, a prominent figure in the lordship. Alexander's cousin, Alan Stewart, Earl of Caithness, was appointed as his military deputy in the north in 1431. A new royal campaign against the Lordship of the Isles began during the summer of that year. Alexander raised a large army to expel Alasdair Carrach and his supporters from Lochaber. Alexander, whom the king had appointed to command the campaign, likely chose to target Carrach in order to secure his own control of Lochaber, which he now claimed as its lord.
The ensuing war resulted in disaster for Alexander. His army encountered a small force led by Carrach and Donald Balloch at Inverlochy in September 1431, where it was heavily defeated. The army of the Islesmen caught Alexander's forces by surprise and routed them from the field, killing the Earl of Caithness and several knights. Alexander, who was allegedly playing a card game when the attack began, escaped the battle on foot and fled towards Kildrummy Castle. Alexander reportedly composed a Gaelic couplet to commemorate his escape from the battle. Alexander's defeat at Inverlochy was followed by the Battle of Drumnacoub, where the men of Clan Mackay defeated the forces of his local allies, led by Angus Murray of Pilrossie. The events of 1431 were followed by several years of peace in northern Scotland, as James I was unable to secure taxation from the Scottish parliament for any new military campaigns.