As with any PLR you need to start with your record card.
Start with Halsbury's Laws (online) to define the terms, take care to read the footnotes if any.
Then use the definitions to search for the case law and/or statute.
If you've got some case law already, if you read through it on WestLaw, at the bottom after 'significant cases cited' etc there will be a list of legislation. If you also read the judgement and obiters the Bench will refer to appropriate statute there too which should get you a good footing.
Then have a sneaky look on Practical Law for 'fiduciary duties' and click around, there'll be some examples, precedents, or maybe even some questions from practitioners on exactly what you need.