Ambush in the sewers

The ambush in the sewers was a trap set by the Bringers for Faith and the Potentials at a supposed weapons cache with Bringers fighting before the trap was sprung and three Turok-Han attacking afterwards.

Background
After mutinying against Buffy, Faith takes command of Buffy's army of Potential Slayers and friends and they interogate a captured Bringer who points them to a weapons cache before Giles kills him. Faith then leads the Potentials there while she sends the Scoobies to find and keep an eye on Buffy which they fail in doing as she's gone by the time they get to the house she was staying in.

The Trap
Faith and the Potentials arrive in the sewers at the weapons cache and are engaged by the Bringers guarding it. The Potentials and Faith manage to win the fight using the weapons they find around them and find a box that they think might contain something important and open it. It turns out to be a bomb and trap that explodes killing a few Potentials and injuring several others including Faith.

Turok-Han ambush
After the explosion the surviving Potentials regroup and gather the survivors to escape when three Turok-Han attack the group with the intention of finishing them off. The survivors try to escape but are surronded by the three Turok-Hans and one Potential is killed. Kennedy tries to fight them off, but is nearly killed before Buffy arrives to help wielding the Scythe and having learned of their predicament from The First. With the Scythe, Buffy proves more than a match for the Turok-Hans and stakes two before decapitating the last one.

Aftermath
Buffy helps the survivors return home where the wounded are treated. Buffy resumes command of the Potentials and her friends and they begin researching the Scythe which eventually leads Buffy to the Guardian's Crypt.