Who or what is Unit 23? Luke Cage must lead his new Thunderbolts deep below on their deadliest mission and face the horrors that mankind can become. While S.H.I.E.L.D. was shut down, a now-missing government squad was charged with guarding a cavern full of impure Terrigen crystals...and if these powerful elements morph Inhumans with wild transformations, what in the world will they do to humans? It's a volatile environment--and a bad time for a challenge to authority from The Juggernaut!