Boyd is hired by the mine to act as security while a trial against them begins. Winona has to put the stolen money back in the evidence locker, but she's going to need Raylan's help to get it there.
But at its heart, this episode is about bonding through crime. Now that Raylan is complicit in Winona's crime, it has brought them closer together, while Raylan is espousing noir philosophy in this scene:
And here, Raylan synopsizes his relationship with Boyd and how, even though their paths normally collide instead of align, there is significant history. Pay attention to that last line: