This is from part one of a two-part self-contained story, starting with the first 6 pages. What's going on when it begins is that Valerian and Laureline are in a telepathic "phase" (Laureline is in space, Valerian is in a café in 1980 Paris), and Laureline is updating Valerian on her progress with her part of their mission (the nature of which will become clear later on).
It may seem like she's just sightseeing, making small talk with aliens and shopping for random knick-knacks, but she's a lot smarter than she lets on, and it's all part of how she digs up information. (A lot of her initial, seemingly off-hand comments turn out to be relevant later on.)
As you might imagine, the series had come a long way since the very first issue in 1967 (collected in Les Mauvais Rêves, "The Bad Dreams"), and I don't know how useful it would be to post it. The only thing you really need to know is that they're agents from the future, sent here to make sure that nothing interferes with the proper course of history (the "proper course" in this case includes a nuclear cataclysm about to happen). A good place to start with the series would be La Cité Des Eaux Mouvantes ("The City of Moving Waters," 1970), but it's unfortunately not available in English either.