Detailed chemical abundances of metal-poor stars offer an observational window to the era of first stars and galaxies. Ultra-faint dwarf galaxies contain a coherent population of metal-poor stars, providing important environmental context to this record of early chemical enrichment. I will present an example of dwarf galaxy archaeology with the ultra-faint dwarf galaxy Reticulum II. Seven of nine stars in this galaxy display extremely enhanced r-process abundances 2-3 orders of magnitude higher than in the other ultra-faint dwarfs. Stars with such extreme r-process enhancements are only rarely found in the Milky Way halo. The r-process abundances imply that the neutron-capture material in Reticulum II was synthesized in a single prolific event, possibly a neutron star binary merger or a magnetically driven supernova. The single r-process enrichment event also provides a unique probe of the star formation and metal mixing history of this galaxy. Reticulum II illustrates how continued observations of faint dwarf galaxies can constrain the very high-redshift universe.
