Viable dagger build?

I'm trying to come up with a good dagger-based hybrid build.

It needs Thief, obviously, for the dagger specialization. However, Thief has few actual combat powers and is comparatively heavy on non-combat utility abilites (lockpick, traps, find treasure).

But now I'm trying to cover both some defense and a way to deal with crowds of monsters.

Weaponmaster, Gladiator and Reaver have multi-target melee attacks, but very little in the way of defense. Reaver probably delivers the most defense of the three due to plate armor, but it'll be hard to get enough strength to actually wear it.

Defender, Paladin and possibly Trickster (Rogue instead of hybrid) have good defense, but lack ways to quickly dispatch groups of monsters.

Any thoughts?

Viable dagger build?