Wilson, Brewster, and Koko's Adventures of Thomas & Friends: The Adventure Begins is an upcoming Chuggington/Thomas & Friends crossover to be created by Stuingtion.
Gordon is unhappy about having to pull goods trains and tells Edward one morning that he won't have to pull them for much longer until The Fat Controller, the railway's director, hires a new engine. (and 3 exchange engines are also called in to help with the work) Later, Gordon becomes stuck at the foot of a steep hill on the main line. With no other engines available, Edward is sent to help Gordon up the hill by pushing the train from behind.
Later, Edward is shunting at Knapford Station when he hears James talking to Thomas, The Fat Controller's new tank engine. As well Wilson, Brewster, & Koko (who are the engines to be working on the line for the while) Gordon is rather sceptical of his size which upsets him until The Fat Controller arrives and asks Edward to teach him how to work in the yard. Initially, Thomas manages to occasionally get in the way, and sometimes causes minor accidents, which Gordon and James seem to sometimes find funny. He also cheekily whistles at Gordon one day while he is resting and wakes him up, much to Gordon's displeasure.
One stormy night at Tidmouth Sheds, Edward tells Thomas about Henry and how he once stayed in a tunnel because of his fear of rain ruining his paint. The following day, Thomas is sent to the Sodor Steamworks where he is repainted blue and given the number 1. Gordon explains that the last #1 engine was a vertical-boilered engine called a coffee pot and orders Thomas to fetch his express coaches. Thomas accidentally tries to take two four-wheeled coaches called Annie and Clarabel, who belong to James. James later returns Annie and Clarabel to the yard, causing Thomas to notice a burning smell before later seeing Henry at the water tower and asks him about his fear of the rain.
The following day, Thomas takes longer to start than usual and arrives at Knapford with Gordon's coaches later than usual. Still cross with Thomas for waking him up, Gordon starts sooner than expected before Thomas can be uncoupled. By the time Gordon reaches Wellsworth, Thomas is worn out and is uncoupled. Back at Knapford the following day, Thomas meets Jerome and Judy, two cranes of the breakdown train while shunting in the yard. James arrives with a goods train and prepares to take Annie and Clarabel, while Thomas again notices the strange burning smell which is coming from James' wooden brake blocks.
The next morning, Henry isn't able to leave Tidmouth Sheds and Thomas is instead asked to pull his train. Unfortunately Thomas starts too soon and leaves the coaches behind, much to The Fat Controller's dismay. Thomas returns and is coupled to the train, but Gordon, James, and Henry tease him about it at Tidmouth Sheds later that night. Edward kindly offers to let Thomas take a goods train for him the next day. However, Thomas gets too excited to take Edward's advice about the Troublesome Trucks which leads him to almost have an accident and The Fat Controller orders the two engines to stay in the yard at Knapford until Thomas knows enough about trucks as Edward does. During this time, Thomas manages to help Henry overcome his fear of rain.
A few days later, Thomas and Edward are in the yard when James rushes by because the Troublesome Trucks are pushing him, causing his wooden brake blocks to catch on fire. Thomas senses he is in trouble and puffs after him. Thomas attempts to couple up behind James' train to slow him down, but the trucks' speed and weight cause James to derail on a bend before Thomas can couple up. Thomas returns to Knapford and fetches Jerome and Judy to rescue James who he takes to the Steamworks. Later that night, everyone congratulates Thomas, even The Fat Controller who announces that after a few repairs, James will have proper brakes and a new coat of paint and Thomas, due to his unselfish bravery and heroism, will have his own branch line. Everyone is happy for Thomas, except Gordon who asks who will fetch their coaches because tender engines don't shunt until The Fat Controller says the other engines will have to fetch their own coaches until he finds another small engine who can.
A few days later, James returns to the yard with new brakes and a fresh coat of red paint and Thomas is given Annie and Clarabel to run his branch line. Arriving at Ffarquhar Station, he meets Glynn the coffee pot engine who asks him to look after the branch line and wear the number one with pride.
During the end credits, various scenes from the "Railway Series" books are shown as the song "Really Useful Engine" plays.