A Matter of Honor
The wife of Alval Uvani wants to end the marriage, apparently due to Uvani's extended absences. He's a traveling merchant whose business often takes him far from Morrowind. Since he is often beyond the Morag Tong's reach (there's that "too far for the Morag Tong" thing again), she has hired the Dark Brotherhood to ensure that the marriage is dissolved, permanently.
Along with your orders you'll find Uvani's schedule. He certainly moves around a lot. You may have encountered him on the road somewhere - he's the Dark Elf that emphatically has nothing to say to you. To keep life interesting, he's well-skilled in the School of Destruction. What Lachance neglects to tell you is that he's equally skilled at Security and Sneak (100 in all three skills) and is a level 15 Battlemage, so it's going to be VERY difficult to get the drop on him. To complicate it even more, he gets a random spell list that draws from the entire School of Mysticism (which includes "Detect Life" in all of its forms). Yep - very difficult to sneak up on this fellow.
You're given one possiblity that might work in your favor. Uvani is allergic to honey, so if you can get him to drink some mead (a drink made from fermented honey, for those who didn't know), you can deal with him quite easily.
The problem is getting him to drink it. He doesn't buy food at the Inns - he steals it. So, like using a Poisoned Apple, you'll need to clear out any food or drink so that the mead is the only thing available to him, which could get you busted and ruin the whole plan. Considering his schedule, that might be a problem since you won't know which inn he's going to want to stop at on which day.
He does return to his house in Leyawiin every once in a while, so you might be able to get the plan to work there. Break in, clean the place out except for bunches of mead, and wait for him to show up (which doesn't happen as often as you might think). If you do go this route, open the safe behind the painting on the second floor. Why would a traveling merchant have a copy of the "Five Tenets" locked up in a secure location?
If patience doesn't work or isn't really up your alley, just try to deal with him on the road between cities. As long as there aren't any guards in the area and you've got cover to block his spells, it's quite doable. Frankly, it's the only plan I've ever managed to get to work consistently.
Once the "divorce" is final, you can pick up your payment and next set of orders from the hollow stump in the garden behind Rindir's Staffs and Edgar's Discount Spells in the Imperial City Market District.