McCoy (DeForest Kelley)’s Timeline and Summary

McCoy breaks into Spock's quarters and impersonates the dearly departed Vulcan before succumbing to the vapors and fainting in Kirk's arms.
We next see McCoy in a bar. He barters with an alien captain for a transport to Genesis.
The alien's voice draws the attention of Starfleet security, who promptly arrest McCoy.
Kirk and Sulu break McCoy out of jail. It's surprisingly easy.
McCoy joins Kirk, Scotty, Sulu and Chekov in commandeering the Enterprise.
En route to Genesis, McCoy takes on more of Spock's personality traits.
After the destruction of the Enterprise, McCoy and the others find Spock on the planet.
Is McCoy caring for Spock or is he technically self-medicating at this point? Ethical quandaries aside, he admits to Spock's comatose body that he misses him.
On Vulcan, McCoy agrees to undergo the refusion and manages to survive the dangerous procedure.
He reunites with Spock at the film's end.