Maya,a young television reporter, works for New India Television. Radharamanan, the Managing Director of the channel, has a fascination for Maya, who was brought up in an orphanage by Father Chanthakkadan. Maya takes up the responsibility of bringing up a few orphans whom she has picked up from the streets. One of these kids is Devan, who is sort of a child prodigy, with a computer-like mind and very good in studies and extra-curricular activities. R. C. Shekhar, a scientist, lives very near their house, with his servant Damodaran. He is working on a project, which could help in making human beings invisible. On the very day that he successfully experiments his 'magic' potion on a rabbit, he is urgently called to the U.S as his daughter, who is studying there, meets with an accident. Meanwhile, Maya's friend and lover Roy, also a journalist, is in jail after having been framed in a murder case by some influential politicians including the State Revenue Minister Divakaran, another minister Yunus Kunju, the Police Commissioner Shanmughan and the very influential Kuwait Nazar. With the help of the newly appointed Collector Anita Williams, Maya shoots a video of these baddies accepting millions of rupees as commission from some Arab businessmen, who are there to sign some business deals with the State Government. Maya immediately goes to Radharamanan and shows him the clip. Radharamanan is thrilled and agrees to telecast it, after discussing it with the Board of Directors. Somehow Nazar, Divakaran and others come to know of this and they go after Maya, in order to get from her the memory card containing the clipping. On the very same day that R.C.Shekhar goes to the U.S, Maya is abducted by Nazar and group. The kids are baffled. Anita Williams, Father Chanthakkadan and Radharamanan know who are behind this, but nothing can be done without sufficient evidence. And then Devan, who had seen R.C. Shekhar conducting the experiment on the rabbit, steals into Shekhar's lab and drinks the potion. He becomes invisible and sets out to save Maya. Devan did manage to save Maya, but when yunus tries to shoot Maya, Devan comes in between and gets shot. Due to the potion he gets saved but as side effect of getting shot he turns into a gigantic monster and kills those who has done wrong to him and his family. After killing the baddies, Devan leaves Maya and the children and makes his abode in the deep ocean, with an end note saying that "to fight for the Justice, Devan will come back as Athisayan".
Athisayan was released in Kerala during the summer vacation, on 17 April 2007, mainly aiming at children. The target audience of the film were school children, whom the makers of the film expected to come in large numbers to the watch the new superhero. Athisayan was a flop at the box-office, despite the huge promotional activities prior to its release. The evident resemblance to Hulk and the comparison to this proved costly for the film. Also the family audience preferred films like Vinodayathra and Big B which released at the same time. The film received mainly negative reviews. It received a rating from Nowrunning.com. Metromatinee and Sify.com also gave mainly negative reviews to the film. The makers actually planned a sequel for the film, had Athisayan become the new superhero among children. The last scene of the film states that "Athisayan will come back to fight for justice". But with the poor response to the film at the box-office, these plans are dropped.
