Step 1: Understanding the Question:
The sentence describes a man who abandoned his moral path to satisfy his ambition and consequently faced a terrible fate. We must find the error.
Step 2: Detailed Explanation:
Let us evaluate the structure and idiomatic expressions used throughout the sentence.
Parts (1), (2), and (3) are grammatically correct and flow logically: "He deserted the path of honour in order to satisfy his ambition."
In part (4), the phrase used is "went down his doom".
This is an incorrect usage of English idioms and prepositions.
The correct idiomatic expression to describe someone facing a terrible fate is "went to his doom" or "met his doom".
The noun "doom" refers to a terrible, inescapable fate or destruction. You travel "to" a destination or fate; you do not go "down" it in this context.
For example: "The arrogant villain went to his doom with a defiant shout."
Replacing the preposition "down" with "to" corrects the prepositional error.
Therefore, the error is definitively located in part (4).