A true one-off volume based on the Snowdon Mountain Railway in Wales, following the happenings of three of the Railway's engines - Culdee, Godred and Lord Harry/Patrick.  These engines were never used within a book again, but in spite of this the illustrations are some of the best which Peter Edwards produced within the Railway Series.

Mountain Engine
Sir Handel is feeling surly one evening following lack of co-operation between himself and the coaches.  Rheneas then makes mention that Sir Handel should be pleased he's not on a Mountain Railway, and a small argument breaks out over the workings of a Mountain Railway, until Donald arrives with a real Mountain engine, returning from being mended.  The engine (Culdee) explains the workings of his railway, and then tells the engines a story about a trip on the Mountain Railway before it opened, and how he had to use his wits and use his automatic brakes to avoid an accident.
 
Bad Look Out
After Duncan has a near-miss and is accused of keeping a bad look out, Culdee draws on the story of Godred to enlighten Duncan.  Godred's conceit got him into trouble, believing he could rely on his automatic brakes for absolutely any purpose, and was generally reckless.  Until one day, as he descended from the summit, rolled over and off the track and tumbled down the hill.  Afterward, Godred was brought back and since the Railway had no money to mend him, he was used for spare parts instead, until eventually, nothing else was left of him.  While this generally frightened the life out of Sir Handel and Duncan, Skarloey and Rheneas weren't keen on telling them that Culdee had made the story up!
 
Danger Points
Culdee is delivered home again and catches up with his old friends again.  But there is discontent in the yard, with the presence of Lord Harry, the new number six.  Culdee comments on Harry's recklessness, whilst Harry justifies it with being modern and "up-to-date" and Culdee reckons it's more conceit than just being Harry's "super-heat".  He proceeds to ride roughly up the mountain with his coach, which results in an accident where his coach derails at some points and Culdee has to rescue him and his passengers.  The manager reprimands Lord Harry and in the end, takes away his name as punishment, as well as taking him off passenger duty until further notice.
 
Devil's Back
No.6 doesn't take to his new duties of taking "The Truck" to the summit, and complains about it to the others, who remind him of it's importance.  And on a windy day, he has to use every ounce of bravery he as to perform a rescue operation and save some climbers from the mountain.  He sees it as an opportunity to prove himself to the others and the Manager, and in spite of feeling anxious about it all, he performs the action admirably.  So much so that No.6 is honoured by the climbers for being their hero and named after a member of their group who in spite of sustaining injury himself went out of his way to help his friends.  The book is concluded with closure on Patrick's reformation, how he is still brave and ready to take risks, but knows only to do it in states of emergency.