Croft, portrayed by Angelina Jolie, finds herself deep within an ancient Egyptian tomb, on a quest for a precious diamond located at the far end of a chamber. As she approaches her prize, a large robot ambushes her, leading to a thrilling chase and a fierce battle. Using her quick thinking, she disables the mechanical beast by tearing out its motivational circuits. Upon seizing the diamond, she discovers it’s not just any gem—it’s a memory card labeled 'Lara's Party Mix.' Curious, she inserts it into a laptop hidden within the robot, bringing forth a soundtrack of music. This intense scene is later unveiled as merely a training session within Croft's practice arena at home, expertly programmed by her assistant, Bryce.
On this significant day, the first phase of a planetary alignment is set to occur, leading up to a rare solar eclipse that happens only once every 5,000 years. Meanwhile, in the secluded city of Venice, a shadowy group known as the Illuminati searches for a crucial key to rejoin the halves of a mystical artifact referred to as the triangle. Mr. Powell, a member of the Illuminati, insists they are close to success, yet he seems utterly clueless about the key's actual location.
Croft's loyal butler, Hillary, attempts to engage her with various projects, but her mind is elsewhere, still grieving the loss of her father who mysteriously disappeared years ago on May 15. This date weighs heavily on her heart. Later that evening, Croft is haunted by a dream, recalling her father's cryptic words about the planetary alignment and an enigmatic object known as the Triangle of Light. Waking suddenly, she hears a clock ticking and discovers a hidden chamber in her home, where a carriage clock inexplicably begins to tick, revealing an underlying mystery.
In seeking answers, Croft visits Mr. Wilson, a clock expert and friend of her late father. She suspects the device is linked to the Triangle of Light, but Wilson denies any knowledge of either. Shortly after, Croft encounters Alex West, another tomb raider, whose unscrupulous approach to treasure hunting repulses her, even as a unique chemistry develops between them. That night, a mysterious figure named Wilson contacts her, revealing that he recommended her to Manfred Powell concerning the clock, although unbeknownst to Croft, Wilson is part of the Illuminati.
The subsequent day, Croft confronts Powell at his home, showing him photographs of the clock, quickly discerning Powell’s deception when they meet. Later that evening, armed commandos storm her residence, raiding the house and stealing the clock despite Croft's attempts to repel them.
The following morning, Croft receives a heart-wrenching letter from her father, strategically set to arrive after the alignment begins. Within, he uncovers that the clock is indeed pivotal in retrieving both halves of the Triangle of Light. This powerful item, harboring the potential for both immense good and unfathomable destruction, had split into two parts after causing devastation in an ancient city worshipping its magic. Croft's father implores her to find and obliterate both halves before the Illuminati can exploit their power.
In Cambodia, West begins to piece together the puzzle of the triangle's retrieval, yet it’s Croft who ultimately succeeds in snatching the artifact and escaping a colossal six-armed guardian statue that confronts her. They arrange a meeting in Venice, now in possession of the very pieces needed to complete the Triangle. Powell extends a tempting offer to join forces but reveals a dark family secret: Croft's father was once an Illuminati member, a claim she vehemently denies.
As tensions mount, Croft cautiously agrees to travel to Siberia alongside Powell and Bryce. In an ominous tomb, they discover a massive model of the solar system that activates with the approaching alignment. After successfully securing the other half, a shocking betrayal unfolds when Powell takes the desperate measure of murdering West to force Croft into completing the Triangle. With a heavy heart, Croft fulfills the daunting task, utilizing a singular grain of sand cleverly hidden within the clock.
As the Triangle is completed, its immense power is unleashed, resulting in a chaotic struggle between Croft and Powell, with her ultimately outmaneuvering him. She is then thrust into a surreal alternate dimension where she meets her father's spirit. He urges her to destroy the Triangle rather than use its power for personal gain. Moved by his words, she refuses the temptation of changing the past and returns to confront her reality—where time begins to rewind to the moment of West’s murder.
In a daring move, Croft seizes the chance to reverse the knife's trajectory, eliminating the Triangle's threat by destroying it. This act restores the flow of time, redirecting the blade back into Powell's shoulder during their escape from the collapsing chamber. In a final confrontation, Powell taunts Croft about her father's death, but she fiercely fights back, avenging her father's loss and reclaiming a cherished pocket watch containing a picture of her mother.
Upon her return to the mansion, Hillary and Bryce are taken aback by Croft’s unexpected transformation, as she appears wearing a beautiful dress. She pays tribute at her father's memorial in the garden before returning inside. There, Bryce has reprogrammed their assistant, SIMON, offering Croft a fresh challenge, while Hillary presents her with her beloved pistols, which she accepts with a knowing smile.
