What was the mystery?
It's a unique-headed bug in the enigmatic family Enicocephalidae. These soil-dwelling insects are predators of other arthropods. They are of phylogenetic interest as a potential sister lineage to the remaining Heteroptera, the true bugs.
Enicocephalids aren't terribly common- I can count on one hand the times I've seen them in the field- and I was most surprised to find one scurrying about under a stone in my small urban front yard.
Five points to James Trager, who first picked the order. And five more to Kojun, who got the family.
Ha! I run into these occasionally and always thought they were young of some sort of reduviid. Taxonomy fail on my part!