The Days of Future Present is a crossover that occurred in several annuals in 1990.
Franklin Richards is supposed to be a young boy at this point in the mainstream Marvel Universe. Yet, it seems as if an older Franklin has somehow appeared. With this revelation begins the Days of Future Present, a mystery of who's who and what's what.
In Franklin's future, the mutants are hunted by Ahab and his hounds so as to allow the humans to rule the planet. During a Sentinel attack, Franklin is killed but sends a dream self into the past. There he feeds off the powers of his younger self, as well as Rachel Summers, a past girlfriend. His presence also awakens Ahab, a man who sleeps on the border of here and now; a gatekeeper of realities; someone who wants to keep the future as it is. Ahab releases futuristic drones and Sentinels in an attempt to quell any adverse effects older Franklin's presence will have on the present and future.
The future Franklin does not understand that he is a dream version of himself and tries to manifest things to be as he remembered them. He transforms the Four Freedoms Plaza back to the old Baxter Building, makes X-Factor's Ship vanish, and reconstructs Xavier's Mansion, all are acts that alert various groups to Franklin's presence. These teams, the Fantastic Four, X-Factor, the X-Men, and the New Mutants, must band together to figure out the mystery of the future Franklin. They must also thwart the odd machinations of Ahab, as he in turn wants a piece of older Franklin.
During the fighting, younger and older Franklin see the awesome destruction that is possible if Franklin is allowed to keep his powers. They decide to lock younger Franklin's potential inside so that all power is inhibited, thereby eradicating the older Franklin's future of Sentinel enforced human dominance from the timelines.
Ahab captures Cyclops and Sue Storm and turns them into his hounds, a process that "permanently" changes their DNA. They hunt down older Franklin, Rachel Summers (his girlfriend), and Christopher Summers, whom Franklin had stolen from Cyclops in an effort to get Rachel some acceptance.
In the end, Ahab is thwarted, the dream Franklin dissipates, Rachel uses the Phoenix Force to reconstruct the DNA of Cyclops and Sue Storm, and each team is able to return to their respective corners of the universe.
The Fantastic Four
Mr. Fantastic and Sue Storm get to see their son grown up. They must also come to grips with the fact that, according to this particular timeline, Franklin dies in a future far more bleak than they had imagined. Younger Franklin's powers are released before the dream Franklin departs, but the boy now has a look at what his powers will be capable of performing.
The slow trickle of X-Men returning is seen and a new face, Gambit, is introduced.
The New Mutants
At one point, older Franklin returns to Xavier's school. There he dreams up his old classmates, the future's version of the New Mutants. This version stumbles upon Cable's New Mutants. Franklin's team appears to have a mutant who resembles Doug Ramsey, an old teammate of many of the current New Mutants. Not only does this foreshadow a possible resurrection of this character, but the New Mutants must watch their friend be taken away again when Franklin makes his team disappear.
Rachel Summers comes face to face with Jean Grey after a confrontation with older Franklin. Rachel finally admits that she is Jean's daughter from the future. Jean and, to an extent, Cyclops, have a hard time accepting this news. Rachel must deal with her emotions of being rejected while Christopher, her kind-of half-brother, is fully accepted by both parents. The story ends with Jean contemplating where her feelings towards Rachel really lie.