Reprint of and retroactive backup story to The X-Men #121 - Shootout at the Stampede! (May, 1979).
At a burger joint near an abandoned chemical factory, Cyclops has stopped in to get burgers for himself and some of the other X-men. Outside, Wolverine confronts Jean Grey about her obvious attraction to him; though she denies it, Wolverine advises that she can't just hide her feelings and she needs to deal with it.
She replies that she will deal with it, then, and suggests that one of them should leave the X-men. But before she can elaborate, Cyclops comes outside and the two stop talking and stare at him. As he asks why they're staring at him, Jean changes the subject by saying that she's sensing someone in trouble at the old factory, to which she carries them all telekineticly.
At the factory, Jean says she senses 10 tenants living in the lofts of the factory and one mindless nervous system living below it. Wolverine notices that the ground is shaking, and as it opens up beneath him and Jean, she calls out to Cyclops to evacuate the tenants from the building.
Buried in the subterranean labyrinth of ducts and machines beneath the factory, Wolverine and Jean realize that there's a powder-keg of volatile chemicals irresponsibly left behind by the old factory owners. As they try to make their way through the darkness, they are beset by a mutated life form that has adapted to the toxic environment of the factory; when Wolverine slices one off of Jean, it splits into four smaller versions of the same creature.
Without having anyway to fight them, and worried they may blow up the whole building if they do, Jean and Wolverine are soon completely buried in the creatures; though they're protected by Jean's telekinetic force-field, the field becomes uncomfortably tight as the creatures crowd in against it. As Jean starts to feel panicked, Wolverine suggests that there are certainly worse ways to go, so she might as well just enjoy it.
Finally receiving telepathic conformation from Cyclops that the tenants have been evacuated, Jean lets lose the power of the Phoenix force and blows up the building around Wolverine and herself. As the two of them emerge unharmed from the flames, Cyclops asks Jean if she's okay and if it was horrible.
Wolverine and Jean just look at each other for a moment, and he walks away commenting that it was the "Best time I've had in months."