After getting off of the train, Barret hints the purpose of the next
mission, then tells everyone to meet back at the base. Head west and
go upwards. Talk to the kid by the fence, (there's a Save Point
nearby, too) then head west again. You will now be in the Sector 7
Slums. Barret clears out the bar and the team heads inside. Talk to
the people here, then check out the bar.
In the bar, you'll meet Tifa, who is also a member of Avalanche, as well
as Marlene, who is supposedly Barett's daughter. If you bought the flower
you can give it to either Tifa or Marlene. Then talk to the others. Barett
shows up when you try to leave and reveals the hidden base underneath the
bar. Talk to Tifa, and go down to the base. Cloud and Barret get into an
argument and whan Wedge tries to restrain Barret, he gets beat up for his
efforts. Return to the bar. Tifa follows and asks Cloud to join them.
Tifa reminds Cloud of their promise, then Barret comes up and pays Cloud
the 1500 Gil. Barret then agrees to pay 2000 for the next mission.