With a Cabal Fleet making its way towards Mars, the Guardians have to find a way to make it onboard the High Command ship, which is surrounded and protected by many cabal warships. Zavala decides to take a page from the Cabal's tactics by leaving subtlety at the door: detonate a cabal ship's nuclear reactor, cutting a hole in their defenses that would allow a shot at boarding the Command ship. Cayde approves of this plan.

With Rasputin distracting the Cabal on one side, the Guardians sneak aboard a warship on the opposite flank and make their way towards the core. Once they find it, the doors around them shut:

Primary Heat Exchangers
Thanatus Adtracto VII

The room has a large circular shape, with doors along the entire top level, and a large pool of reactor coolant on the bottom level. The Core is in the center, surrounded by six electrical generators that rise from the depths in unison.
The guardians must all jump down onto the top of each generator and analyze it with their Ghosts to try to overload the reactor. An alarm begins to blare, and the generators all begin to fall towards the coolant. The Guardians must jump out onto a platform that surrounds the pool.

Activity begins to happen on top of the Core, and a Psion with an ornate headdress appears: Tenok, Psion Flayer. Two large metal shields opposite one another rise, and deploy four energy shields around him as the encounter begins, and Cabal begin to pour in from the upper platform.

For the duration of the encounter, Guardians can stand on the top platform (but will have no cover from the cabal), on top of the lower platform surrounding the pool (providing them with moderate cover from the cabal above), and on top of the generators when they rise from the coolant. At the center of each generator is a panel that the player can deploy their ghost on to try to overload the generator (holding it in place).

There are two ways that the encounter can be completed, depending on the actions of the Guardians.

Method 1:

While the Guardians hold off the Cabal coming in from the top platform, at least one Guardian must jump onto one of the generators and deploy his ghost. While his ghost is deployed, the Generator's movement is greatly slowed as the Ghost struggles against Tenok for control of it. Cabal will be shooting at the Ghost, so the Guardian must remain on the platform to protect it from attack. If the Guardian leaves the platform, his Ghost will leave the generator, giving control back to the Flayer, which will lower it back into the coolant for a period of time.

Tenok's shield is directly tied to the generators. He is flanked by six shields, two of which are metal, and they rotate around him at different intervals. If a Guardian is hacking a generator, the shield adjacent to it will be weakened (assuming it's not one of the metal shields). The more generators that are being hacked, the weaker the shields will be, and the more damage that Tenok will take. And the longer that a Guardian is on top of the generator, the longer Tenok will be vulnerable to the team's weapons and Supers.
But the longer a Guardian is on top of the generator, the more he is exposed to the Cabal on the upper level (which can also jump down to the bottom platform). Not only that, but the longer the generator is outside of the coolant, the more it will overheat. There are four blue lights on the outer edge of each generator. After the generator has been out of the coolant long enough, the lights will start turning red. It takes three seconds for all of the lights to turn red once the first one lights up, after which the Generator will quickly plunge into the coolant, killing the guardian on top if he does not jump out. Tenok can only focus on one generator at a time, so the generator that begins to light up first is random, but they will all light up one after the other.

Players must communicate to the player(s) on top of the generator(s) which one is lighting up before they are killed. It's up to players whether they want to jump off one by one as their platform lights up (to maximize damage), or if they want to jump off as a group to play it safe. The amount of enemies (and their variety) is directly tied to fight duration; the longer the fight goes on, the more difficult it will become. Once Tenok reaches half health, more Phalanxes will begin to enter, threatening the players safely on the platform. Tenok's shield will also begin to rotate at ten second intervals, making it necessary to have more than one generator hacked to ensure that sufficient damage is being done in case a hacked platform is adjacent to the metal shield.

If players do enough damage and Tenok is killed, his shields will fall over, allowing Guardians to jump to the central platform that he was on and deploy a Ghost (after collecting their loot drop), which will lock the doors (preventing the arrival of any additional Cabal waves, though players will have to finish off the survivors) and lower the stairs on the far back of the room, leading back to the Guardian ships. The player's Ghost will also hack the reactor, emptying the pool of coolant, and overloading the reactor. Players will then have to run out to their ships before the reactor blows.

Trophy/Achievement for killing Tenok with weapons and hacking the Reactor:
Chill Out
Dude, you really need to... (Bronze Trophy/5GS)

Method 2:

Far riskier, but the fight can be over much faster.

At any point in the fight (but ideally at the beginning, when players can coordinate on the generators, and before the Cabal numbers become overwhelming), all Six Guardians can jump on and hack the generators simultaneously. This will initiate the "Overload" buff. When this happens, Tenok will be greatly vulnerable to damage, but the Guardians will have no cover from the Cabal above. The two Guardians on the platforms adjacent to the metal shields should focus on the cabal above while the rest of the team does damage to Tenok. Shortly after a third of his health is depleted (he will let out an echoing screech when his health hits exactly one third, but players can continue to fire if they wish), he will pull himself into the system. Players must jump off the generators as fast as they can, since he will force control back and plunge all six generators into the coolant a second after he disappears.

Enemies will begin to spawn faster, as Tenok returns back to the central console, clearly weakened. The generators will come back up one at a time, giving players a short window (that repeats if missed) to hack all of them simultaneously once more. If done successfully, players will be granted the "Overload x2" buff. Tenok's shields will begin to rotate slowly, so players will have to alternate between doing DPS and focusing on the adds. Once he's down to a third of his health, he will once again pull himself into the system, causing the generators to plummet.

He will once again appear at the console, and an alarm will begin to blare. If players are able to take complete control once more, they will have the "Overload x3" buff, which will drop his energy shields completely. The two metal shields will begin to spin quickly around him, and the generators will begin to lower and raise sporadically, making it more difficult to land shots on him (but they will not fall into the coolant). Once his health is depleted, he will let out a final scream as he tries to enter the system once more, but will explode into a hail of arc energy, killing all Cabal on the upper platform (and causing any surviving Cabal to drop a blue Engram), ending the encounter (without requiring a Guardian to deploy his Ghost on the central platform). Ghost will tell the Guardians that the reactor has become highly unstable, and they should evacuate as quickly as possible. Explosions will rock the ship as the Guardians must sprint towards their ships, jumping over rolling debris and around obstacles.

Trophy/Achievement for killing with Overload x3
Adiós, muchachos.
This area's gonna be a cloud of vapor the size of Nebraska. (Silver Trophy/10GS)

Notes:

While players can get the Overload buff at any point in the fight, they must successfully trigger Overload x3 to obtain the alternate ending, which can only be done if the first overload is done before the first third of Tenok's health is gone. Otherwise, players will only get up to Overload x2 (which can still end the fight faster, if done successfully). Needless to say, to be successful with Method 2, all Guardians must stay alive at least until the Overload x3 has begun.

If a player dies on top of a generator, his Ghost will continue to hack the generator, but will be vulnerable to gunfire. Another player can jump on the Platform to protect it, but must not forget that the timer is still running. Once Overload x3 has begun, Ghosts will be temporarily invulnerable to enemy fire, giving the surviving players a chance to complete the mission.