The Assimilation Crisis occurred in December 2006, HST. Agents Iskillion, Tawaki, and Hul had meant to take a Star Trek Spock!Sue to the Genesis Planet, but they were in a hurry, and a redshirt noticed them. They wound up on a Borg Cube in the Gamma-Delta Quadrant border. Tawaki dropped the lirpa he used for a crutch, and the Collective was alerted to their presence. Hul and Tawaki were assimilated.
When that happened, the Borg Alarm went off. Agent Tadkeeta spread the word and a group of agents portalled in. The failure to neuralyze the Enterprise crew had altered the timeline (Sisko was now a Borg), and so some of the agents went to do the neuralyzing.
Others stayed to rescue the Borg and neuralyze the Collective. Six more agents were assimilated and two were killed before they could be rescued and the Collective neuralyzed.
Hul lost his mind, and the next time he met Tawaki he threatened to kill him.
A total of twenty-one agents were involved in the Assimilation Crisis. They are listed in order of appearance from the top down, left to right. (A) indicates the character was assimilated, (S) indicates the slain.