Walter Lavelle was a British Army colonel and a member of the British Rite of the Templar Order during the 19th century. While the Assassins were aware of Lavelle, they considered him of little interest.
On the morning of the 1842 retreat from Kabul by the British to Jalalabad in Afghanistan, Lavelle was approached by a corporal named Cavanagh who was secretly aware of his Templar connections and sought to take advantage of them. The corporal took Lavelle aside to suggest that they desert as he foresaw the massacre of their forces which were mostly comprised of untrained civilians. Outraged, Lavelle initially rebuffed Cavanagh but by nightfall had soon changed his mind when the Afghans made their first attacks.
The following day, Lavelle, Cavanagh, who Lavelle had ostensibly taken as his batman, and a loyal sepoy left the company to make their own way to Jalalabad. During the journey, the three men were faced with a small encampment of five Afghan hillmen and were forced to fight. Lavelle and the sepoy provided cover fire from behind a boulder as Cavanagh used the element of surprise to attack the tribesmen directly. When an errant shot allowed one the Afghans to get in an attack, Cavanagh walked away from the conflict with a permanent facial scar and a considerably low opinion of Lavelle's abilities.
Concealing themselves in the hillmen's clothes, the three deserters later stumbled upon a roaming settlement of one of Afghan leader Akbar Khan's warlords. Unable to simply flee, the disguised Cavanagh and Lavelle made their getaway when Cavanagh used his command of Pushtu to tell the Afghans that the sepoy was their prisoner and the pair left him to die.
When the two men finally reached Jalalabad, they claimed that they had gotten lost after becoming detached from their cavalry unit. Though everything about Lavelle gave rise to rumors that the colonel and his batman had deserted, Cavanagh's own prowess in combat deflected suspicions.
Years later, Cavanagh had returned to England and become a Templar himself. Soon after Lavelle had him nominated for membership in London's Travellers Club, Cavanagh recommended to the Order that Lavelle be executed and took care of it personally.