At first, you might have trouble with developing the key question, but remember there are no limits to your imagination except those you put on yourself. The real value of your key question determines the direction your novel will take and selection of an intriguing subject advances your path to your reader if the reader has an interest in the subject described on the book cover.
For example: A book containing the story the remaining two women and one man after a pandemic strain of the Bearing Sea influenza has more reader appeal than an investigation into mysterious aardvark road kills.
Armed with the vital question, it is time to expand the central plot idea into a beginning, turning points, and the ending. Turn lose of your creative nature and let your mind explore the possible endings that you might use for your book. If you work on the ending first, at least you will have a destination to direct your plot. Later, in the plot development process, you might change the ending to one of your original alternatives or develop another one.
Next, work on the beginning. This is where the reader discovers the Protagonist (main character) of the book. Here the reader gleans an idea what direction the book is heading and determines the nature of the problem presented by the Antagonist (villain or sinister group) or the circumstances directly opposing your character's ability to achieve a mission or objective. In the beginning portion of the book, the author sets the time, season, location, and extenuating circumstances vital to the reader's understanding of all that follows. Often, the author plants a significant thought, element, or detail for use in resolving the challenge presented in the plot.