The Third Way

The Third Way is the final storyline mission in Grand Theft Auto V. The mission is triggered if Franklin chooses the option C (deathwish).

Overview
The mission begins with Franklin at the "F" marker on the map shortly after the final heist on the Union Depository Tower. Devin Weston shows up at Franklin's house and attempts to convince Franklin to kill Michael De Santa. After Devin leaves, the player is given a set of three options on his cell phone. Choosing C leads to this mission.

The mission sends Franklin to the home of Lester Crest. Franklin and Lester come up with a plan to avoid having to kill either Michael or Trevor Philips. They lead the FIB and Merryweather into a trap at the foundary under the pretense of melting down the gold there from the Union Depository heist.

Franklin picks up Lamar Davis and they go to the foundry. Lamar acts as lookout while Michael, Trevor, and Franklin team up to kill all of the FIB agents and Merryweather mercenaries sent against them. Various stages of the ensuing battle require that the player provide backup to certain characters. First, Lamar will radio that he's being overrun and needs help. Franklin must get out to the place where he dropped off Lamar and kill the FIB agents attacking him before he dies or the mission fails. Then Michael must go over to where Trevor was positioned to check on him. Trevor gets back up and Michael and Trevor must fight their way out of the foundry and help Franklin kill off any remaining FIB and Merryweather forces in the area.

Finally, the three characters devise a plan to kill off the various factions trying to kill each of the characters in an attempt to take the heat off themselves. They all go after a target they weren't directly involved with to throw off suspicion.
 * Michael is sent to kill Stretch as revenge for betraying Franklin and Lamar in Lamar Down.
 * Trevor is sent to kill Steve Haines for betraying Michael in The Wrap Up.
 * Franklin is sent to kill Wei Cheng for betraying Trevor in Bury the Hatchet, torturing Michael in Fresh Meat, and interfering with Trevor's business interests.
 * Once the above targets are eliminated, Trevor goes to Devin Weston's house to kidnap him.  Trevor must fight his way through Merryweather security forces to kidnap Devin.

Killing Stretch
Stretch is found on a basketball court with several gang bangers around. He's relatively easy to eliminate and his homies are mostly packing pistols. Kill him with a melee attack to get a Gold medal.

Killing Steve Haines
Steve is found on the ferris wheel on the boardwalk shooting a video for a TV show. Him and a camera man are in one of the ferris wheel cars. Approaching too close to the ferris wheel will alert Steve and fail the mission. Trevor must pick off Steve from a distance. The bright lights and cluttered area around the Ferris wheel can make this a difficult shot. After killing Steve, Trevor must lose the cops before heading after Devin. Kill Haines with a headshot to get a Gold medal.

Killing Wei Cheng
Wei Cheng is found surrounded by body guards near a series of vehicles. As soon as Franklin arrives, his body guards get him into a sedan and attempting to escape while shooting at Franklin from their SUV's. If Franklin acts quickly, he can kill Wei Cheng before he leaves the parking lot and save himself from having to chase down the fleeing convoy on the highway. Kill Cheng with a sticky bomb to get a Gold medal.

Killing Devin Weston
After Trevor fights his way through the Merryweather security forces, he finds Devin hiding in a trunk near the pool. Devin is pulled out and carried to his Tornado in the drive-way. Trevor throws Devin in the trunk and goes to meet up with Franklin and Michael.

After some dialogue, the three protagonists push the Tornado with Devin in the trunk off a cliff and into the ocean below, then the car explodes.

Trivia

 * After you help Lamar fight off Merryweather Soldiers outside of the warehouse, he is nowhere to be found and isn't seen leaving the area after the soldiers are all dead.  However, Franklin talks to him on the phone afterwards, proving that he survived the shoot out.
 * After completing this mission, each character will receive their cut from the final heist in The Big Score.
 * It's likely that this is the canon ending since the scene where the three protagonists look into the trunk of Devin's Tornado is depicted in the official artwork "The Trunk".
 * This ending is seen by many fans as the "true ending" to Grand Theft Auto V and most probably is. The other two endings are likely only available as some players would like to kill Trevor or Michael, and Rockstar wanted to give them the choice to.
 * Franklin is tasked with kiling Trevor's antagonist, Wei Cheng.
 * Trevor is tasked with killing Michael's antagonist, Steve Haines.
 * Michael is tasked with killing Franklin's antagonist, Stretch.
 * This is the first time in the GTA series where all the major antagonists are killed in the same mission.