Some of the universe's most extreme explosions leave behind almost no trace. The original explosion is unseen, but our observations can capture the long-lived echo it leaves behind as the shock front plows into its surrounding environment. In new research accepted for publication in The Astrophysical Journal, we have discovered what may be the clearest example yet of one of these hidden explosions: the radio afterglow of a powerful gamma-ray burst whose initial blast went unnoticed.