By the Book

By the Book is a main story mission in Grand Theft Auto V given by Federal Investigation Bureau (FIB), involving protagonist Michael De Santa and Trevor Philips.

It's the 24° GTA V mission in chronological order, and it takes place in Los Santos.

Michael and Trevor combine to locate a target for the FIB.

Gold Medal Objectives (100%)

The following are the Mission Objectives required to obtain the Gold Medal in the mission "By the Book":

Don't Stop Me Now: Complete without Mr K's heart stopping.
- Don't allow Kerimov's heart tare to pass 200 BPM.
Electrocutioner: Electrocute Mr K.
The Tooth Hurths: Pull out Mr K's tooth.
Wrenched: Hit Mr K with the wrench.
It's Legal!: Use waterboarding on Mr K.

Note: You can complete each Gold Medal requirement in multiple playthroughs of the mission. You don't need to obtain them all in one single playthrough.

By the Book - Mission Details:

Michael or Trevor (whoever you are playing as) will receive a call from Steve Haines, telling them to go to a warehouse in Banning. Michael, Trevor, Dave and Steve all meet at the location. Devin Weston is also there but leaves as soon as Michael and Trevor get there.

Ferdinand is then brought out by Steve. He wants information on Tahir Javan, an Azerbaijani man who Steve believes to have close links to terrorism. Knowing he is about to get tortured, Ferdinand tells the group that Tahir is at a house in Rockford Hills. Michael and Dave head out to investigate the house, leaving Trevor and Steve behind with Ferdinand.

Upon arriving at the house, Dave notices they've been given a false lead. He calls Steve to let him know. Play switches back to Trevor who now has free range to torture Ferdinand for information. The ways Trevor can torture him are:

Pulling out a tooth with pliers
Electrocuting him
Hitting him with a wrench
Waterboarding

Once the first round of torture is complete, Ferdinand will reveal Tahir is actually at a house in Chumash. Play switches back to Michael, who travels to the house with Dave. On the ride over, Dave reveals he's been pretending that Brad is alive and sending letters to Trevor. He wants Michael to keep an eye on Trevor.

Once at the house, the pair park up on the other side of the road to avoid detection. Michael sets up a sniper rifle and asks for a description. They notice a party going on in the house and need extra information on his description as multiple could fit the description. Extra information given through various torture sessions is:

He's average height, average build and middle-aged
He has a bushy beard
He's a chain smoker, particularly smoking Redwood Cigarettes
He is left-handed

From the information given, Michael is able to narrow down who Tahir is and assassinate him.

The play switches back to Trevor. Steve tells him the task is done and that Trevor can dispose of Ferdinand. Instead of killing him, Trevor drives Ferdinand to the airport. Ferdinand wants to go back to his family in Morningwood but Trevor doesn't let him go, saying he now has to flee. Trevor drops Ferdinand at the airport, despite his condition from the torture, and drives off.