Aparichithan movie revolves around three college girls who are very close friends. Meenakshi (Kavya), Devi (Manya) and Simi (Karthika) are very good friends. Once they get caught for stealing the question papers for the exam and were expelled from the college. As they did not want to go home.
Simi's boyfriend Chacko (Vineeth Kumar) with the help of one of his friends find a guest house for the girls in Nelliyampathi, in the middle of the forest. But on their way they meet with an accident and are forced to walk a long way through the forest.
They meet Raghuram( Mammootty) a wild life photographer from USA who was taking pictures of a rare bird for National Geographic channel in the forest. Initially the girls didn't like him but later they became friends.
Raghuram tells the girls about Kalyani, the village chief's daughter that he had met during his stay in the village. He also informs them that Kalyani who had a good resemblance with his sister, just disappeared one day.
The rest of the movie flips back and forth creating a climax and reveal the past of Raghuram as the story unfolds.