Who's Whose?

Who's Whose? is an entertaining and straightforward guide to the most commonly confused words in English today, with real examples of good and bad usage to make differences crystal-clear. The Embarrassment Rating
involved in each mistake is included, together with an explanation of
why the confusion happens and how to avoid it in the future.

So
if you mistrust (or distrust?) your spellchecker and want to maintain
or improve your written English, this is the perfect companion for you.