The Formation is the first episode of Season 1, and the entire Before & After The Adventure Begins: The Prequel Series.
In February 1914, Bertram Topham Hatt went to the Sodor Government Forming Meeting of 1914, where the Sodor Government made a contract that the Sodor and Mainland, the Wellsworth and Suddery and the Tidmouth, Knapford and Elsbridge would be formed into one whole railway. Topham Hatt agreed and signed the contract.
The opening was declared on 28th February 1914, where all the S&M, W&S and TK&E engines attended. Topham made a speech first, then declared the North Western Railway opened.