The Fall is one relational plot which is not (necessarily) a love story. Falls to temptation, as the Medieval Church knew, can come in many forms: greed, gluttony, sloth, lust, envy, jealousy. Think Othello, Hamlet, Macbeth.
1. Once again I have combined this plot with temptation because that is where it often begins. It is not simply pride that goes before a fall, but temptation, when we succumb, that can lead us into despair, paranoia, madness and suicide. When we give into the temptation to greed, lust or envy, (or lying, cheating or stealing), we risk a fall. Real life does have consequences.
2. Then again, the beginning might be simply life circumstances that we can all (potentially) relate to such as the discovery of a spouse’s infidelity or the loss of a job. Think “going postal.” Imagine a whiskey bottle dragging a person to perdition, as in the lost weekend. Imagine being “mad as Hell and I’m not going to take it anymore.” The fall can come when life throws that proverbial curve ball and we get beaned.
3. A third approach might be beginning the story on the fringes of society (I might say on the edge of respectable society). Imagine the loner, the loser, the homeless bum that may be…? Some people are already living a fallen life. Others revel in excess and extreme living. There is no telling what is out there in the dark, or maybe just around the corner.
This storyline considers the exaggeration of emotions we see when they are set free from normal social and moral constraints. In particular, fear and/or hopelessness or helplessness (if not madness) are often strong in the story. It considers the extremes human beings are capable of going to and the excesses that can invariably cause us to stumble and fall. Again, like last time, society does not like to lose so there often is not a happy ending. Read Poe. Redemption, though, is possible.
Unless you are considering the third approach above, you might want to start by moving your character from as normal, average, common (everyone can relate) a life as possible to going off the deep end. To do that, I recommend (for the sake of a strong hook at the beginning) that you begin with some hint or foreshadowing of what is to come. The opening goes to the breaking point, when the **it hits the fan. Consider the story of King David. He is happy, successful, everything is going his way until he catches sight of Bathsheba sunning herself on the roof across the way…
In the middle, we watch in horror as the person sinks slowly or rapidly into their obsession – paranoia, schizophrenia, madness. Perhaps they don’t fall quite that far, but the condition appears hopeless and we wonder how this person is ever going to get out of this bind. David tries to manipulate Bathsheba’s husband, and fails. He finally sends the man into the front lines in battle to get him killed. Suddenly, David is not only guilty of adultery, he is guilty of murder; and every step takes him deeper into the pit.
In the end, Othello kills his wife and kills himself. David faces a rebellion by his own son. He kills his son and yet, somehow he finds redemption. There is not necessarily a tragic ending here. But there will be resolution. Think of it like a sickness. The cure may require strong medicine so if the disease doesn’t kill you, the cure might. Still, there is a chance for recovery.