Sometimes, your worst enemy can prove to be your greatest ally, as long as he can be trusted not to kill you.

As Echo Bourke, newly graduated member of Fleet's Special Services rescue squad, looks forward to her first assignment she desperately wants to prove herself, but never does she believe that her first mission could be her last.

The war with the Tolleani rolls onward and the Federation is at the mercy of an insidious biological weapon that has the potential to decimate humanity. A small group of scientists held captive in enemy territory, has a possible solution.

Echo is sent to Persephone, a dark, alien moon drenched by incessant rain, the air poisonous and every land surface brimming with life so aggressive that just being there is to place yourself at risk. And hidden within that living morass is the greatest of all secrets.

From the beginning, the mission does not go as planned, becoming worse as Echo realizes the greatest threat to success comes not from the enemy, but from within her own squad.

Captured by the Tolleani she learns that Barbus Koll, the alien who destroyed her entire family, is also present on this tiny, deadly world. When she discovers the true purpose of the mission, she fights to deal with her overpowering desire for revenge. Finding herself alone, she joins the most unlikely of allies in her efforts to salvage what remains of the mission. But can he be trusted? Can she, alone, complete her mission without losing her own life?