This study guide specifically refers to the following trilogy:

Mezieres, J.C.; Christin, P.; Tranle, E. Valerian and Laureline: The Ghosts of Inverloch; Cinebook, Cantebury, Kent, 1984. Kindle AZW file.

Mezieres, J.C.; Christin, P.; Tranle, E. Valerian and Laureline: The Wrath of Hypsis; Cinebook, Cantebury, Kent, 1985. Kindle AZW file.

Mezieres, J.C.; Christin, P.; Tranle, E. Valerian and Laureline: On the Frontiers; Cinebook, Cantebury, Kent, 1988. Kindle AZW file.

Valerian and Laureline, agents for the Spatio-Temporal Agency, are trying to save the future of Earth after a series of events erase all signs of the Earth of the future and the Spatio-Temporal Agency.

In the first novel of this three-part series, The Ghosts of Inverloch, Valerian is on the planet Glapum't. He knows that he is supposed to capture one of the planet's inhabitants, a Glapum'tian, but he does not know why. He has had no contact with Galaxity, which concerns him. He uses several methods before finally capturing the Glapum'tian, later identified as Ralph. Valerian picks up Ralph and heads for Earth in the 1980s.

Meanwhile, the Spatio-Temporal Superintendent is in Galaxity, a future city of Earth, while the entire city is fading away. He remains to consider the situation, then leaves. Laureline is on Earth in the 1980s. She is a guest of Lady Charlotte and Lord Basil Seal. Lord Seal meets with CIA agents and learns that virtually everyone who has a connection to their nuclear programs has become insane. Everyone of those people has one of three ordinary objects nearby.

Lord Basil returns home just as Lady Charlotte gathers a group of people, including Valerian, Laureline, Ralph, an Earth agent named Albert, and three aliens called Shingouz. Lady Charlotte announces that they are to witness the arrival of the ghost who haunts Castle Inverloch. and she takes them to a deserted part of the castle where they see the Superintendent arrive via a portal.

In the second novel of this three-part series, The Wrath of Hypsis, the Superintendent tells Valerian and Laureline that there are problems on Galaxity. Because they are from the future, Valerian, Laureline, and the Superintendent know that a nuclear disaster will almost destroy Earth in 1986. The group sets out for the polar region where Albert has identified four ships that might be involved in the pending nuclear disaster. Using Ralph's telepathic abilities and his conversations with a pod of killer whales, the group zeroes in on a ship called the Hvaxdet. When they get near the ship, it takes off in flight, making Valerian's group certain they need to follow it.

They soon chase the ship to ground on a planet called Hypsis, where they find three entities. There is a father, a son, and a machine referred to as the ghost, which Albert and Lord Seal soon identify as the Christian Trinity. The Dad reveals that they own the solar system that contains Earth. According to Dad, the other rulers of Hypsis are not happy that Galaxity has constantly interfered in actions across the galaxy. Dad has destroyed Galaxity but calls a halt to his plan to destroy Earth, which Albert points out was the original catalyst for forming Galaxity.

On the Frontiers is the final novel of this three-part series. It begins as Valerian meets another Spatio-Temporal agent, Jal, who was on a distant galaxy when Galaxity disappeared. That galaxy protected him from the fate of everyone else who is from Galaxity. Jal survived, but the woman he loved did not. Jal is trying to set the Earth back on its former course toward the devastating nuclear event so that Galaxity will return, bringing his woman back with it. Jal struggles with the ethics of his actions and finally gives in to his need for solitude, remaining alone while Valerian and Laureline continue their journey without him.