FBI Agent Karen Ennen was sent from Washington DC to Dick Tracy's city as part of the investigation of a murder at a traveling circus. She had dark hair and sharply-defined features.
The circus had previously been under investigation by the FBI for serving as a cover for international arms shipments. The ringmaster (Ringo) was under Federal Witness Protection, which the murder investigation jeopardized. Due to this, Agent Ennen was operating under instructions to keep local law enforcement away from the investigation (unlike previous interactions between Dick Tracy and the FBI).
She and Tracy were captured by the villainous clown Mr. Pops and placed in a tiger cage. They were rescued and Pops was arrested. Agent Ennen returned to Washington at the conclusion of the case.