Differences from previous iterations in the series are that Lara's environment will be an "interactive world that reacts and remembers", such that footprints left in the mud or mud transferred to Lara's knee from kneeling on the ground will be washed away by rain, the bodies of the foes she encounters will remain where she killed them, and any destruction to the environment she causes will be permanent. According to creative director Eric Lindstrom, this is "to not only reward the player for the effect they're having on the world, but to give them navigational aids." The game uses an animation blending system that allows Lara to interact dynamically with her environment, such as pushing foliage aside with one or two hands, depending on if she is carrying a weapon. It also features a "hybrid lighting model that combines dynamic lights with carefully created light maps" and a weather system that changes the environment, for example, "If Lara's negotiating a wet ledge she's more apt to slip or lose grip," which makes "the environment ... her adversary" for a large part of the game.
Previously seen separate aspects of gameplay have been combined for a new experience. Lindstrom explained that "in the past, there was climbing, and there was shooting, and there was puzzle solving. And they often didn't overlap. We've now integrated all of those elements." This installment also features a new melee combat system, requiring Lara in some instances to use "direct combat and evasive manoeuvres to distance herself from her attacker". Notably, Lara's bike, among other things, will be a key component in solving the puzzles she will encounter in her adventure. Pick-ups will have multiple uses as weapons and tools in interaction with the environment, and Lindstrom stated that Lara "can also split up her guns and fire at two different targets simultaneously," or hold an item with one hand and fire a gun with the other. The grappling hook can now be stretched taut and used to pull objects off ledges unlike in previous iterations, illustrating what project lead Rob Pavey said, that "Lara will be able to do anything that you'd expect her to be able to do," which he called "the big theme this year." Lindstrom describes this as "a philosophy called 'What Could Lara Do?'-WCLD. It's short-hand for having the player be able to use their own intuition about what someone with her abilities should be able to do in an environment such as this, and consistency across the different mechanics and abilities. If she can throw a grenade, then if she can pick up this pole, why can't she throw it?" Crystal Dynamics also aims to make the game non-linear, unlike Tomb Raider: Legend, and eliminate the need for hint icons that indicate the ability to interact with objects.
The interactive cutscenes from previous titles have been replaced with "adrenaline moments". Instead of specific button presses, time slows down and gives the player a chance to get out of harm's way while retaining complete control of Lara.


Story
The story begins with Lara Croft in the lower corridor of Croft Manor where Lara has to escape from a fire. Upon entering the main hall, she is surprised to see the mansion in flames. As she reaches the main door, Zip shoots at her as Winston tries to restrain him. The game flashes back a week into the past, showing Lara in the Mediterranean Sea. Lara is searching for a way to Avalon, the mythical resting place of King Arthur, and the place where Amanda claimed Lara's mother is. Lara finds a temple of "Proto-Norse" origin, leading her to believe that Avalon and the Norse underworld of Niflheim are one and the same. She also finds a gauntlet that belonged to the Norse god Thor. Lara is attacked by mercenaries working for Amanda, who take the gauntlet to Amanda's boat. After pursuing them to their ship, Lara encounters Natla, whom Amanda has in captivity. They began discussing Lara's find and Natla states that Avalon is the same as Helheim, rather than Niflheim as Lara had supposed, and that Lara will need Thor's hammer, Mjolnir to enter. The ship begins sinking due to an explosion caused by one of the mercenaries in a firefight with Lara. Lara shoots at a fleeing Amanda who throws the gauntlet into the sea. Lara quickly jumps to catch it, letting Amanda escape.
Lara travels to coastal Thailand, as Natla had suggested, where she discovers that her father had already been there and took Thor's second gauntlet back to a hidden study beneath Croft Manor. After retrieving the gauntlet, as well as a map showing the location of Thor's belt and hammer, Lara is surprised to find the manor going up in flames. An injured Zip, assisted by Winston, shoots at her as he thought Lara had shot him after taking Amanda's "Wraith Stone" from the vault. Lara and Winston convince Zip it was not her and Lara tells them to get out of the mansion while she goes to view the security video in the computer room. Before she does, however, she is confronted by a doppelganger resembling herself, apparently created by Natla. The doppelganger shoots and kills Alister, who was trying to escape the flames, then flees. Lara carries Alister's body out of the house, and resolves to continue searching for Mjolnir, which she believes will give her the power to kill Natla. In Mexico, Lara retrieves Thor's belt, which powers the gauntlets needed to wield his hammer. After retrieving the belt, she heads to Jan Mayen Island and finds Mjolnir in Valhalla. She also finds a message from Odin, Thor's father, saying that he will need to perform a ritual before Thor can open the way to Helheim.
With the gauntlets, belt and hammer, Lara confronts Natla on Amanda's second ship. Lara reluctantly agrees to work with Natla, who claims to know Odin's ritual. Lara travels to the Arctic Sea and, with Natla's help, opens the entrance to Helheim. She soon encounters her mother, Amelia, who has been turned into a thrall, a deceased individual whose corpse is reanimated by the substance eitr. As the mindless thrall approaches, Lara forces her back into the eitr. Lara kneels in sorrow as Natla appears to reveal that she was using Lara and Amanda to gain access to Avalon, via Thor's hammer. Natla also reveals that she killed Lara's father, Richard, when he refused to cooperate in this task years ago. The doppelganger appears and restrains Lara just as she was about to attack Natla with Mjolnir. As Lara is about to be killed, Amanda appears and uses her Wraith Stone to defeat the doppelganger. She also holds off the approaching thralls allowing Lara to continue.
Lara finds Natla activating a massive, ancient device at the heart of a titanic cavern filled with eitr. Natla explains that Jormungandr, the Midgard Serpent, refers to the network of tectonic divisions spread across the world beneath the oceans giving rise to the legendary interpretation and that this device sits right atop where the supercontinent, Pangea, had split apart millions of years ago. The device is designed to bring about Ragnarok, or what Natla refers to as the Seventh Age, by triggering apocalyptic levels of volcanic activity throughout the world.
Lara destroys the device with Mjolnir then hurls the hammer at Natla, who is distracted by trying to repair the machine. Natla is struck down and plunges into the eitr. Lara heads back to Amanda, but they discover that the exit is blocked. Lara spots the portal that originally brought her mother to Helheim, realizing that her mother may not have known how the device had worked thus remaining trapped. Lara and Amanda work together and escape.
They are teleported back to Nepal, where Lara's mother accidentally teleported herself to Helheim. Amanda attempts to stir up a fight with Lara, who chastises her. Amanda contemplates her choices, before finally limping away. Alone, Lara says goodbye to her mother, and the game ends as she walks away from the portal.