Toxic Deduction. Holmes & Watson, #6

Patrick O'Brien is convinced someone is trying to poison him. But the business tycoon doesn't know who in his inner circle it might be. Could it be his husband Toby, tired of years of playing second fiddle to him? Or Helen, who kept his nightlife business afloat for years but now finds herself on the outer? Perhaps Vincent, the young genius behind Patrick's burgeoning social media enterprise who believes he's owed a larger share of the company? Or could it be Strap-On Anna, a notorious dominatrix whose skill Patrick enjoys, but who resents the control he maintains over her? There is only one person who could possibly work out which suspect is truly evil.
The investigative lawyer Holmes, of course. And what better way to solve the crime then to invite everyone for dinner and hash it out, over a few too many glasses of wine? Coming back from a medical conference the following day, John Watson gradually draws from Holmes the full story, the anger, resentment, and hate of those forced to live around Patrick O'Brien. How on earth did Holmes solve this case before dessert?