Ash and friends finally arrive at Castelia City, They find a Venipede only to have a whole swarm invade the city. Meanwhile Giovanni is headed to the Unova region to see the progress Team Rocket has made there. After the swarm passed Professor Juniper arrives and requests the assistance of Ash and co. Ash decides to put his Gym battle with Burgh on hold to help the Professor.
Professor Oak's Live Caster: Yamask
Who's That Pokemon?: Venipede (US)
Although, in Japan, it was shown that Ash, Iris and Cilan went with Professor Juniper to the Desert Resort, in the English dub she went alone while Ash and the gang stayed for the next gym badge against Burgh. Basically they skipped the scene in which Ash and co. go in the helicopter due to the next two postponed episodes.