The film starts with Lara Croft training in an Egyptian room. She can see her prize but as she approaches it, she is attacked by a robot larger than herself. The robot, which is called S.I.M.O.N., was designed and built by Bryce, her electronics assistant, for her to practice with. She battles with it, eventually ripping out its cables to disable it. She then takes her prize- a memory card labelled ‘Lara’s Mix’ and she uses S.I.M.O.N. to play it.
Meanwhile in Venice. On the first day of the planetary alignment, Mr Manfred Powell is in front of the Illuminati High Council and is assuring them that he will find the first half of the Triangle of Light, an artefact powerful enough that gives the holder the power to control time and change events. However, Mr Powell has no idea where it is or how to find it.
15th May. Lara is in her father’s study. She reminds Hillary that today is the date on which her father was pronounced missing. That night, Lara dreams of her father and he tells her of the Triangle of Light and of the clock, which is the key to getting the two halves of triangle. She wakes to the sound of ticking and follows it downstairs, to a hidden room under the grand stairs. She breaks in and retrieves a carriage clock but discovers that it is working anti-clockwise. Bryce examines it and they discover a smaller, handheld clock inside, with the All Seeing Eye symbol in the middle.
She heads off the next day to see Mr Wilson, a horologist and a good friend of her father. He states that he does not understand what it is but passes her the name of Mr Powell as he might do. When she leaves, he apologises to a photo of her father; he is part of the Illuminati and knows that he could be putting Lara in danger, which was against her father’s wishes.
She goes to Powell, taking with her photographs of the clock as she does not trust him. He pretends that he doesn’t know anything about the clock, but when Lara returns home, she tells Bryce that she knows that he was lying. That night, whilst Lara is performing some bungee ballet, a group of commandos invade the manor. Lara is able to whittle the group down but they manage to steal her clock.
The next day, Lara receives a letter from her father, written before he died and was ordered to be sent after the start of the planetary alignment. It tells her the history and power of the triangle and that she can find the first half of the triangle in Cambodia, along the Khmer Trail. His final words to her were to find and to destroy it.
When she gets to Cambodia, she sees Powell with her clock, Alex West, an old friend, and local men pulling down a stone figure to get into the Tomb of the Dancing Light. Once in, Alex believes that he has figured out the first part of the puzzle, but Lara tells them of the location of the ‘true eye’ where the clock must go. Powell ends up trusting her and throws her the clock. She activates a swinging log and is able to grab the first half from here. She makes her escape, not before battling a huge six armed stone guardian statue.
Powell telephones her and they agree to meet in Venice, pairing up as partners to collect the second half. He also lets her know that her father was part of the Illuminati, although she doesn’t believe him.
They travel to Siberia, to the second Tomb, the Tomb of Ten Thousand Shadows. After examining the large Orrery in the cavern, Lara discovers that the second half of the triangle is in the Sun. Using the clock once again as the key; she is taken into the Sun.
She delivers the triangle to Powell, and with her assistance once again- killing Alex as persuasion, he completes the triangle. Here, she finds herself and Powell running for the triangle up the side of a pyramid. She wins and finds herself in a crossing of time, her present with her father’s past. Lord Croft explains to her that she has to destroy the triangle once and for all as it is dangerous. She agrees reluctantly and returns to present day, where time has been frozen. She turns Powell's knife on himself and destroys the triangle. The cavern starts to collapse but before Lara can escape, she fights unarmed with Powell, killing him and retrieving her father’s pocket watch from his body. She escapes through the tunnels with her sled dogs.
Back at Croft Manor, Lara, in a white dress, visits her father’s memorial in the gardens. Returning inside, she discovers that Bryce has fixed S.I.M.O.N. and Hillary has her trademark dual pistols ready for her, which she takes.