This section contains a summary of Babylon 5's story arc (the 5-year plotline) up to, but not including, "Messages from Earth." Note that this is chock full of spoilers!
"Matters of Honor" brought Marcus Cole, a Ranger, to the station; he led Sheridan and Delenn to a new ship, the White Star, a combination of Minbari and Vorlon technology. Pushing the White Star to its limits, Sheridan destroyed a Shadow cruiser. Londo attempted to sever his ties with the Shadows. Morden met with a Psi Cop, apparently far from the first such meeting.
The Centauri sent a replacement for G'Kar to the station in "A Day in the Strife" and threatened to persecute the families of G'Kar's supporters unless he gave up his exile and faced trial. Meanwhile, Ta'Lon, a Narn whose life Sheridan saved some months earlier ("All Alone in the Night") pledged to act as Sheridan's bodyguard. Londo arranged to have Vir sent off to Minbar as the new Centauri diplomatic liaison.
In "Passing Through Gethsemane," Lyta Alexander, the station's first telepath and the person who unmasked Talia's Bureau-13-implanted personality, returned from a stay on the Vorlon homeworld to become Ambassador Kosh's attache. The Vorlons appear to have modified her, possibly even enabling her to carry one of them inside her.
The conspiracy of light made its move against President Clark in "Voices of Authority" by releasing a recording of Morden and Clark planning Santiago's assassination. Ivanova located another race of First Ones and secured a promise of help in the fight against the Shadows.
G'Kar learned of Londo's involvement with the Shadows in "Dust to Dust." He was sentenced to prison for assaulting Londo, and was visited in a dream by Kosh, who posed as the Narn deity G'Lan.