The team scrambles to find the group responsible for an assassination attempt on a UN diplomat. Whelan and Reyes find a key clue in the depths of the city's tunnel system. Stabler struggles to balance the investigation with his mother's increasing need for support. 

When DNA from an SVU rape investigation connects to an OCCB unsolved murder, Stabler and Benson uncover a revenge-for-hire scheme on the dark web. While Bell and Jet follow the money trail to expose the website's anonymous creator, Stabler asks Professor Rollins for help with a key clue.