It is a special day for Harold -- the Northern Lights will shimmer over Sodor at sunset! He cannot wait to share this moment with his engine friends on Lookout Mountain. However, Thomas and the gang have a busy day ahead of them, which is impacted by damage to the Sodor Suspension Bridge. Carly and Sandy warn the excited engines that they should only cross the bridge in case of an emergency -- a rule that is ignored by Kana, Diesel, Nia, AND Thomas! When the bridge finally collapses and prevents them from reaching Lookout Mountain in time, Harold selflessly chooses to help his friends instead of see the Lights. His sacrifice teaches the young engines an important lesson: your actions add up - stay away until it is safe to play.