By the Book

"The media and the government would have us believe that torture is some necessary thing. We need it to get information, to assert ourselves. Did we get any information out of you? Exactly. Torture's for the torturer...or for the guy giving orders to the torturer. You torture for the good times - we should all admit that. It's useless as a means of getting information."

- Trevor Philips

By the Book is a mission in Grand Theft Auto V, given by FIB agent Steve Haines to protagonists Michael De Santa and Trevor Philips.

Mission
Michael or Trevor (whoever is being played at the time) receives a phone call from Steve Haines telling them to go to a warehouse and meet the other protagonist (the mission automatically begins with the receipt of the phone call). There, they find Haines and Dave Norton along with Mr. K. Haines wants Michael to assassinate Tahir Javan, an Azerbaijani man who Haines and Norton claim has ties to terrorism. Mr. K previously set up an audio-visual system for Javan and so is the FIB's sole source of information. Haines orders Michael to go with Norton to locate Javan, while Trevor and Haines remain in the warehouse with Mr. K.

Michael and Norton drive to their first location, a home in Los Santos, but this turns out to be a false lead. Haines then orders Trevor to torture Mr. K in order to discover Javan's whereabouts. There are four ways in which Trevor can torture Mr K: (Mr. K can't be pushed too far. If this happens, he'll need an adrenaline shot, which requires injecting him with a syringe. Mr. K can die up to three times before Trevor runs out of adrenaline) The first round of torture reveals that Javan is actually at a beach house in Chumash. Michael and Norton drive to the home, but once there, they discover that a party is in full swing and that there are several men present who could possibly be Javan. At this point, Haines orders Trevor to engage in more torture. Through three additional rounds of torture, Mr. K reveals that Javan is: Through these clues, Michael is able to identify Javan and assassinate him.
 * Waterboarding
 * Beating him with a wrench. Where Trevor hits depends on his position as he observes Mr. K. All three areas have the same effect and damage. Mr. K's left = knee. Middle = genitals/midsection. Right = arm.
 * Electrical shocks from a car battery
 * Extracting a tooth using pliers. First tooth changes speech. Unknown if more pulls either further deteriorate his speech or nothing at all.
 * A man of average height and weight (Able to kill Javan at this point to complete the mission early.)
 * Has a beard
 * Is a chain smoker and left handed

Back at the warehouse, Haines tells Trevor that Mr. K is expendable and orders Trevor to kill Mr. K after Haines has left. Once Haines departs, Trevor instead decides to free Mr. K. He guides Mr. K from the warehouse and into a waiting vehicle, at which point he drives Mr. K to the airport.

Mission Objectives

 * Go to the warehouse in Banning. - (Michael or Trevor)
 * Go to Rockford Hills. - (Michael)
 * Choose a tool to torture Mr.K. - (Trevor)
 * Go to Chumash. - (Michael)
 * Choose a tool to torture Mr.K. - (Trevor)
 * Locate the target. - (Michael)
 * Choose a tool to torture Mr.K. - (Trevor)
 * Try to locate the target again. - (Michael)
 * Choose a tool to torture Mr.K. - (Trevor)
 * Kill the target. - (Michael)
 * Take Mr.K. to the airport. - (Trevor)

Gold Medal Objectives

 * Don't Stop Me Now - Complete without Mr. K's heart stopping.
 * If Mr. K's heart gets over 200 then it will stop.
 * Do waterboarding 4 times to get this easily when replaying. That's the one with the least damage.
 * Electrocutioner - Electrocute Mr. K.
 * Do this first to prevent killing Mr. K.
 * The Tooth Hurts - Pull out Mr. K's tooth.
 * Do this closer to the end.
 * Wrenched - Hit Mr. K with the wrench.
 * This can kill Mr. K if it is the last weapon, but it is unpredictable as Trevor can swing anywhere.
 * It's Legal! - Waterboard Mr. K.
 * Hold down on the bumper to prevent extra pressure.

Los Santos Shepherd Newspaper
"''A beach front house party turned into tragedy yesterday when an Azerbaijani-American was killed, in what appeared to be a professional job by a long range sniper. Police are baffled by the case not merely because they are baffled by most things, but also because no motive is apparent. The man Tahir Javan an Azerbaijani-American in his late 40s moved to this country when he was 13 and grew rich in the green energy sector and has subsequently donated large sums to education initiatives here and his former country. Who would offer a professional hit on him and why, or whether this was a professional hit or a psychotic rank gone dangerously wrong is still unclear. Tahir was a smoker, a bon vivant and a lover of life and all that was precious. "Why would anyone want to kill him? He didn't have any enemies, just friends and friends he hadn't made yet. We all loved him," Said partygoer Rachel Withers who described herself as something big in greeting cards.''"

Bleeter Posts

 * @chumash_kiki - "Omg police everywhere! Guy got shot at a party next door. What does this mean for Chumash property prices???"
 * @alderneyedwin23 - "White supremacists carry out professional hit on Azerbaijani man in Chumash. At least that's what me and my roommate are telling everyone."

Glitches

 * Should the player re-play this mission and have Trevor wearing a full outfit with shoes, during the mission his pants will revert back to his default jeans, but he will have no feet.
 * Also, while replaying the mission, if the player kills Javan early, the game will rarely bug and Michael will stand still aiming, the player will not be able to switch to Trevor and there's no Mission Failed screen. The only solution is to pause and load a previous game file.
 * After torturing Mr. K. for the first time, the player switches to Michael drinking coffee with Dave. Sometimes, the player will be able to control Michael before the cutscene actually ends. If this happen, the cup of coffee Michael had will be stuck in his hand.

Trivia

 * This mission is said to be the one of the most controversial content in the whole franchise, and has received heavy criticism by critics from various media outlets.
 * In the Japanese version of the game, when Trevor tries to pick any of the torture tools, he ignores all of them.
 * The gold medal objective "Don't Stop Me Now" is a reference of a popular song by Queen, which has the same title.
 * This mission can be triggered by Michael or Trevor, though after receiving the phone call as Trevor, the player will be prompted to switch to Michael. After the usual "perspective change" animation, the opening cutscene of the mission starts playing with Trevor and Michael together, regardless of where Trevor might have been when he received the phone call.
 * The name of this mission its from a sentence that Trevor says while he is drowning Mr. K, he may say: "Always go by the book, that's my motto.".
 * The gold medal objective for waterboarding Mr. K called "It's Legal!" is a reference to the CIA using waterboarding as a form of interrogation and infamously denying that it was torture.
 * It is possible to assassinate Javan early (before getting all the information) successfully, to cut the torture session short. However this does not change the outcome of Mr. K's condition as he will still walk with a limp and have altered speech even if neither the wrench or the pliers were used on him. Doing this provides a bewildered response from Dave, and a few unique lines shared between him and Michael.
 * If the player switches to Michael immediately after the mission ends, Michael will be in front of the FIB Headquarters saying goodbye to Dave.
 * If Trevor has tortured Mr. K enough to death and does not inject the adrenaline shot on the latter; a cutscene triggers as Steve berates Trevor for overdoing the brutality inflicted on Mr. K. Haines would also say "At the exact moment I get bored with you, your little racket will end", this is one of the exact references that Haines wants Trevor to be disposed. The mission also fails.