When Alfred Bester came to Babylon 5, he claimed to have information through his connections at the Psi Corps about a shipment of "weapons supplies" heading for their mutual enemy, the Shadows. Bester knew that the Shadows had plans for his telepaths, and thus used the station's crew to take control of it and save his people aboard. He used the cover story of "weapons supplies" to get their help.
The White Star tracked the ship down in hyperspace with the help of Bester's talent, destroying its escort of Shadow Fighters. After the escorts were destroyed, a full-size Shadow Vessel appeared, yet did not fire on the ship and retreated. The crew took control of the transport and took it back to Babylon 5.
On the station, they opened the ship up to find its pilot - who had committed suicide rather than be captured - and its cargo of cryo-preserved telepaths. Among the telepaths was Bester's lover, Carolyn Sanderson. They had all been modified with unknown Shadow tech, including wetware implants in the skull that allowed them to merge with computer networks.
The crew placed the telepaths in cryo-freezers in the Medlab facility, offering to keep them alive in return for Bester's help. From the events of the battle, along with information uncovered by Garibaldi in the Book of G'Quan, they were able to deduce that the Shadow vessels were susceptible to telepathic interference. That was why the ship did not fire on them; Bester was aboard the White Star. With this information, they began looking for ways to utilize their newfound weapon against the enemy.