Phaseolus vulgaris lemurum
Appearance: essentially, it’s an Undead bush colored a particularly unpleasant shade of mottled white, brown, and purple. The bush is mildly mobile, but moves very slowly. Zombeans are digestable, vaguely nutritious, and (barely) edible.
The Zombean menace started up a little while back. The affected plants have been infected by a mutated version of the tobacco mosaic virus; the virus is spread by contact, and can zombify a regular common bean bush within twelve hours. Once transformed, the new Zombean bush will then pull itself out of the ground and go looking for other P. vulgaris plants to attack via twining and pulling. There is currently no cure for the Zombean virus.
All of which is probably terrifying, if you’re a bean plant. But for humans, it’s just a problem; the Zombean virus is utterly harmless to any animal life-form, and the plants are not aggressive towards animals. Zombeans also infect only one species of bean plant, at the moment, and while it’s an extremely common species the situation promises only to be mildly disastrous and exceptionally expensive. So they’re throwing lots of money at the problem, as is the way of things.
And that’s where your team comes in. The team working on the problem haven’t gotten much in the way of results yet, but they have determined that the Zombean virus is artificial in origin. Does it really need to be said why it’s now vitally important that whoever made this abomination of science be tracked down? After all: if the person or persons who created it did so because they didn’t like green beans, then what do they think of other plants? Or, well, human beings?