Given the task definition and input, reply with output. In this task, you're given five sentences, numbered 1 through 5, and two options a and b for possible titles for the story. Your job is to choose the title that better fits the story. Indicate your choice by 'a' or 'b'.

Sentence 1: Jay was an undercover police officer. Sentence 2: He spent the last 2 years deep inside a gang. Sentence 3: He was building a case against the gang overlord. Sentence 4: The overlord had committed over 2000 crimes under Jay's watch. Sentence 5: Jay managed to film lots of this and hoped to apprehend the overlord. Choices: a. Undercover work. b. Marionettes.
a