Brothers
Released in April 2011, Brothers, is the first episode in Big Finish's second Highlander season / series.
Kronos has captured and imprisoned a Watcher. He decided to relate his true history to the hapless prisoner before killing him.
Kronos was the head man of a forgotten tribe. One night his tribe was overwhelmed by an outside force that included an Immortal. The leader of the raiders captured Kronos and forced him to watch as his people and home were destroyed. Finally the leader's last act was to slowly strangle Kronos to death. As Kronos died his only real regret was that he had not enjoyed the pleasure and power of slowly murdering another person as his killer was enjoying Kronos' own death.
Kronos woke to find himself impossibly alive he set off to find his killer only to encounter a band of Immortals lead by a seemingly wise Immortal named Dilijan. Dilijan took Kronos under his wing for a time explaining the basics of immortality but leaving out the vital information regarding Quickenings. Dilijan was worried that the knowledge of Quickenings and the Game would encourage Kronos' brutal bloodlust before Dilijan's brainwashing through trepanning could give him the chance to calm and control Kronos.
Sometime later Kronos and Dilijan's band of immortals came across the trail of the group of raiders that had wiped out Kronos' people. Dilijan allowed Kronos to confront his killer, hoping Kronos would achieve satisfaction and be content to learn more peaceful ways afterwards. Instead, after Kronos killed the bandit leader, he befriended the lone Immortal in the band, Silas, who revealed the nature of the Quickening. Kronos turned on Dilijan.
Methos had joined Dilijan's band not long before, as Silas and the raiders attacked, Methos convinced Kronos to take him on as an ally. Dilijan watched in horror as all he had created was murdered and ruined.
Sometime later Kronos, Silas, and Methos found Dilijan again. Dilijan had married and settled in a village. They were a peaceful people, and with no Immortals he had no one to brainwash through Quickenings. Kronos ordered rape, murder, and burning the village and salting the ground. Before murdering -though not permanently killing - Dilijan again Kronos promised to find him every fifty years to destroy his world.
The three became four when Caspian joined them. Time went on and Kronos was satisfied. Or mostly satisfied. He would make Methos play Chaturanga (Sanskrit: चतुरङ्ग; caturaṅga), an ancient Indian strategy game commonly theorized to be the common ancestor of the board games chess, shogi, sittuyin, and makruk. He had decided that as long as Methos let him win, he did not have to fear betrayal by him. Until the arrival of an Immortal named Kyne at the Horseman's sanctuary changed everything. Kyne manipulated each of the Horsemen until they all agreed to take a sea journey with him. Once the ship was out to sea and far from land, Kyne climbed the mast of the ship and committed suicide, the energy of his Quickening ignited the hold of the ship - packed with lamp oil - and the ship exploded killing and scattering the Horsemen.
Kronos woke on a shore only to realize he was tightly bound. Dilijan explained that Kyne had been his catspaw, he had engineered the destruction of the Horsemen and had created an elaborate network of acolytes and allies to ensure that every time Kronos attempted to rebuild his brotherhood or start a new band from scratch his efforts would fail. Never again would Kronos enjoy the security and satisfaction of his dark brotherhood. Dilijan then left Kronos alone and immobilized on the beach suggesting Kronos not struggle unless he wished to tighten his bonds, though he noted the sun would likely dry them tighter anyway, though the rising tide might loosen them over a few days until Kronos could free himself.
Kronos told his captive Watcher that Dilijan kept his promise, his acolytes continually interrupted Kronos' plans and interfered with his schemes. Further, Kronos managed to access the remnants of the Watcher's database and discovered that Methos lived. He killed the Watcher by exposing him to his engineered toxin, presumably the same virulent disease he had intended to unleash in Paris in the Highlander: The Series episode, Revelations 6:8.