Vlad's plan to get the Left Hand off his own back required the help of The Demon and therefore defeating Terion and Triesco. This left Terion as Vlad's enemy. Terion reminded Vlad of his enmity by trying to shine Kragar while Vlad was his guest.
Ironically, Terion's interference in Vlad's affairs proved to be his undoing. His presence and active enmity stood to compromise Vlad's plan to settle his differences with the Jhereg council, and killing a major Jhereg Organization figure turned out to be a useful part of Vlad's plan too. Terion found himself in the unfortunate position of falling under Vlad's blade after being set up by Vlad and his chief lieutenant, Chesha.