Don's more than a little set in his ways: he has a 7-day meal plan designed for nutritional needs and to perfectly offset his activity level, and his minimal wardrobe is calibrated to his activity level with no concern for fashion or style. He'll make allowances and adjustments as required, but why bother when the calendar is optimized for efficiency?
But Don's also beginning to feel lonely. After a couple disastrous first dates he begins to hone a complicated questionnaire to eliminate time wasted with unsuitable potential partners (smokers, picky eaters). And then a chance encounter and a giant misconception blow Don's whole schedule to bits.
This book is light, funny, and incredibly well written. Don could easily be a bore or a joke or a jerk, but Simsion makes him likeable and sympathetic. You root for him to figure things out, and his endearing challenges make the breakthroughs a glad triumph.