The informant you captured is on your ship and can be interrogated. Hopefully he can give you the name of the spy.
This is a two part mission. The first part takes place in a separate mission instance on board of your ship, during which you'll have to interrogate the man you captured in the last mission. Eventually he will tell you the name of the spy.
In the second part, you will have to defeat the spy in sea combat. He will be around level 34, and will be escorted by two guard ships (both around level 24).
- Defeat the Spy