7aam Arivu

The film depicts the life of Bodhidharma (Suriya), a master of martial arts and medical remedies, who is depicted in the film as the son of a great Tamil king of the Pallava Dynasty. He is sent to China by his guru, who requests him to stop the spread of a pandemic disease existing there from spreading to India. Initially the people in China treated him as an inferior but later when he cures a little girl from the deadly disease and fights against some people who ill treated villagers there, the people of China began to respect and worship him. He begins to teach them how to cure many diseases, the skills of hypnotism and the physical training of the Shaolin monks that led to the creation of Shaolinquan. However, after several years, when he expresses his desire to return to India, the villagers plot to poison him and bury him near the temple, believing that their place would be disease free if he is buried there. Bodhidharma agrees to die and subsequently becomes a fundamental figure in Chinese history, affectionately being dubbed as "Damo".
The film switches to modern-day China, where Dong Lee (Johnny Tri Nguyen) is given the task of starting a government planned biological war against India, known as Operation Red. Dong Lee arrives in Chennai starts this operation by injecting a virus into a street dog. This disease was the one which occurred during the time of Bodhidharma in China. Meanwhile, Subha Srinivasan (Shruti Haasan), a student of genetics researches that Bodhidharma can be brought back to life if his sample of DNA is matched with another sample of DNA which she finds in Aravind (Suriya) a descendant of Bodhidharma who is working as a circus artist nearby. Dong Lee finds out Subha's mission to revive Bodhidharma and plans to kill her first, so that the disease cannot be stopped.
Subha approaches Aravind, but begins to love him and spends time with him, and thereby forgetting about her mission.. One day, Aravind's family see Subha and clearly remember that she visited them a year before to find Aravind and know all about him for the Bodhidharma research. Saving herself, she lies by saying that she doesn't know them. Later that night, Aravind's uncle (Ilavarasu) explains all what happened one year before when they met Subha. Aravind goes and meets Subha, and is enraged upon realising the truth. However the next day, he reconciles with Subha in a love failure mood and agrees to contribute to the research and hence save the country. The research begins of giving life to Bodhidharma and to end Operation Red. But Dong Lee, who is capable of doing anything, does all impossibly bad things, mastered in "Nokku Varmam" (hypnotism), a martial art which was actually taught to the Chinese by Bodhidharma.
Subha goes to her genetics department and announces that Operation Red can be stopped if they read and make use of the cures in a book written by Bodhidharma. However, the department laughs and refuses to believe her, claiming that an ancient book is of no use in modern times. Disappointed, Subha leaves. After some time, Subha and Aravind find out that Subha's professor from the genetics department is assisting Dong Lee in Operation Red. They sneak into the professor's apartment and learn about the operation. The next day, the professor is caught red-handed by Aravind, Subha and her friends, but surrenders and explains that he received a huge sum of money from the China government if he carried out Operation Red. After the professor gives the gang more details about Operation Red and how to stop it, they leave. However, after a while, Dong Lee arrives and the professor once again teams up with him to save his own life.
Dong Lee causes numerous havoc in the city, which Subha, Aravind and their gang barely escape. They finally locate a research centre where they can activate Bodhidharma DNA in Aravind, and decide to hide there for a few days. They all deactivate their phones so that no-one can trace them. But Dong Lee somehow traces Subha and the gang with the help of two of Subha's outside friends. However, he kills both of them afterwards. Dong Lee then locates the place of the research centre. Subha and her friends in the research centre escape in a van, but Dong Lee chases them and the van collapses. An unconscious Aravind gets beaten badly by Dong Lee at first, but then manages to regain Bodhidharma skills somehow and kills Dong Lee. Bodhidharma uses an ancient medicine to cure the disease. Subha and Aravind then get married and finally tell the press about the importance of our history.

Question: How does Dong Lee trace Subha and the gang ?