Complex sentence: Fitz agrees to look into Glekas, but finds that his FBI file has been sealed by an Agent Koutris, who is working for Vondas and tips him off about the focus on Glekas.
Split into simpler sentences: Fitz agrees to look into Glekas, but finds that his FBI file has been sealed by an Agent Koutris. Koutris working for Vondas, and tips him off about the focus on Glekas.