Lord Herbert Lionel Henry Vane-Tempest, a director of the Cambrian Railways, killed in the accident

Plas Machynlleth was the Welsh residence of the Marquesses of Londonderry. It is situated in the market town of Machynlleth in Powys (formerly Montgomeryshire), Wales. It was brought into the family by the marriage of George Henry Robert Charles William Vane-Tempest, Viscount Seaham (and subsequently Earl Vane and 5th Marquess of Londonderry), to Mary Cornelia Edwards, whose father Sir John Edwards had extended and renamed the house.

The house was the family home of the 5th Marquess. His eldest son left Machynlleth on succeeding to the Marquessate, but his youngest son, Lord Herbert Vane-Tempest, remained resident at the Plas until he was killed in the Abermule train collision on 26 January 1921.

The oldest parts of the house date back to the 17th century; the main entrance front was added in 1853. The house was called Greenfields for many years. It was later renamed after the town.