First things first: if any of my players see this, please leave.

I'm writing a courtroom drama session for one of my players to try to get his soul back. The gist of the story so far is one of my players sold his soul to a fiend in exchange for power and to save an ally's life. He has since become something of a high priest for this fiend. Now he is on his redemption story arc and is working with his old god (Selune) to get it back and this is kind of a breach of contract. The party has been served a subpoena to appear in the Diabolical Courts in Phlegethos in 2 weeks (about 2 sessions from now so I have some time to write this).

I already have the endgame worked out and how they can be able to save themselves and win the case through a technicality if their skill, roleplay, and dice rolls are good, but I'm having trouble figuring out the actual flesh and bones of the trial itself.

Any help would be much appreciated.

Is it too much to hope there will be a heavy set fiend in a straw hat who gives the “now, I may be just a small town, country lawyer…” speech?

Start with a normal civil trial.  We’ll skip over a couple steps for the sake of courtroom drama and start on the big day.  Plaintiffs (the devil claiming breach and asking the court for damages) lawyer will make his opening statement, then the Defense.  Then Plaintiff calls witnesses.  Defense gets to cross examine them.  Vice versa, then closing statements and then it goes to the jury.

For the fun parts, theres lots of stuff you can rip off from TV.

At the very least, you should look up what hearsay actually is, if you’re going to be yelling it at your players. 

First, it's most likely the PC received a summons, not a subpoena.  Their records may receive a subpoena, and other party members or associates may be subpoenaed for appearances or or records.  Subpoenas compel to appear as a witness or provide records or other evidence.  Summons  compel to appear in court to answer a charge or complaint.  Warrants can be issued for failure to comply to either.

Quote from TimCurtin >>

Start with a normal civil trial.  We’ll skip over a couple steps for the sake of courtroom drama and start on the big day.  Plaintiffs (the devil claiming breach and asking the court for damages) lawyer will make his opening statement, then the Defense.  Then Plaintiff calls witnesses.  Defense gets to cross examine them.  Vice versa, then closing statements and then it goes to the jury.

For the fun parts, theres lots of stuff you can rip off from TV.

At the very least, you should look up what heresay actually is, if you’re going to be yelling it at your players. 

Thank you, this helped me visualize the process better.

Unless you have a real hunger for a bit with the jury, the judge can also try the case without one.  Might keep the scene more economical.