Jamna Gleamsilver was a gnome assassin and a member of the Zhentarim.
At the start of the Tyranny of Dragons, in 1489 DR Jamna was tasked with a mission to investigate the recent uprising of the Cult of the Dragon. She deduced that they were gathering treasures for the Hoard of the Dragon Queen and boarded a caravan full of hidden cultists that transported parts of the hoard to the final destination. During the journey, Jamna killed a too-curious cultist disguised as a caravan guard.
After the assassination, adventurers could discover Jamna and needed to decide what do with her. She would potentially offer her help against their common enemy.
After the PC's arrive in Waterdeep Jamna expresses her desire to stick with the party until they find the treasure's destination.