The beloved POstables discover a 200-year-old valentine that could change history, while their investigation of a damaged letter leads them to a public figure who could be brought down by its contents. And in the aftermath of Valentine's Day, Oliver, Shane, Norman and Rita are each dealing with heartbreaking circumstances.

POstables seem to be unable to deliver a damaged letter from a military veteran that's a matter of life and death. They've always been able to deliver mail by the grace of God right at the time it's needed most. While Oliver's faith is not shaken, his father Joe questions this divine theory. As Norman and Rita go on a road trip to pursue leads in the urgent veteran's letter, their trip takes them to the next level of their relationship and leads them to the place they're needed the most.

Meanwhile Oliver and Joe go backpacking on a father son bonding trip during which a serious injury puts both their lives at risk. After Oliver doesn't show up at work, Shane spearheads a rescue mission and calls Oliver's police officer friend Dale to help. When all seems lost, what's most important is found. To everything there is a season, a time for every purpose under heaven.