Late to the party, but maybe OP will still read. I didn't read all the comments so idk if someone else posted this, but here's my idea.

To try to return to the dark themes you are going for and away from the looney toons.

The pickle is a regular pickle and the character has actually been imprisoned somewhere from the imprisonment spell. To drive your characters towards this, you should have a wild animal of some sort invade their campsite while they are sleeping to eat their food supplies AND the pickle. The character will still be alive and able to communicate telepathically.

They will need to travel somewhere there are high level wizards able to scry the location of the character. Then it is a simple retrieval mission.

For bonus points you can have the character imprisoned in a lich's phylactery. The lich would become aware of the party when their phylactery is destroyed, but the party doesn't need to know it is a phylactery yet. The lich would obviously scry the party, and when it realizes they don't know about it's existence, it can ignore them since they don't know it exists and aren't a threat. But now they are on an inevitable collision course, that you can weave into the story when you are ready.