On a location with numerous webs, and at least one big spider, there is a something inside a cocoon. It is humanoid in shape, still moving. If the heroes free it (not before they kill or drive away the spiders), they meet a ... zombie!
The poor zombie wandered the dungeon alone, and tried to kill a big living creature (= a spider). The spider used the usual treatment, even if this victim did not look tasty. The zombie can be easily killed as any other zombie. It got but several doses of spider-poison, so can be something worth if it is extracted. You can mention to a druid or ranger the fact the spider had no poison anymore.
The party wakes up in an inn around a table with wine goblets near at hand. They have forgotten all that happened the last day. As they seek to find the truth they come in contact with a man that gives them a job which pays quite nicely.
When they have finished with this rather dubious assignment they are invited to dinner by the the man...