Le Grand Secret (The Great Secret/The Immortals) is a 1989 miniseries co-produced by France, Germany, Spain and Canada and directed by Jacques Trébouta.
Jeanne Corbet (Louise Marleau) is having an affair with Roland Fournier (Peter Sattmann), a researcher working on a cancer treatment in the Paris suburb of Villejuif.
Samuel Frend (Claude Rich), an American secret agent based in France, comes in contact with Jeanne and informs her that her lover is not dead.
The source of the cover-up of Roland's disappearance is revealed: Professor Bahanba (Richard Münch), an Indian scientist also working on a cancer treatment, has discovered JL3, an immortality serum that stops aging and eliminates vulnerability to disease in any living being.
Throughout her search, Jeanne learns about numerous world leaders involved in the cover-up, including Indira Gandhi, Queen Elizabeth II and Ronald Reagan.