Party has been captured by bad guys. They've been left in a cell to rot. They must escape from the cell in order to accomplish any other goals (obviously, purely by the fiction). No one in the party is especially good at picking locks. Guards, if they are present, know not to let the PCs out, but more likely they're just being abandoned here with no guards at all because who cares, the PCs can starve. Digging out would take months, and the party has rations for at most a few days.
That's verisimilitudinous, perfectly in keeping with the rational motivations of some bad people, and contains a single point of failure. No story required.