So I've been working on a mystery novel set at a fictional court in the eighteenth century, and the heroine is a sixteen-year-old princess, incredibly sheltered and naïve. A guest is murdered by her husband after a past affair (on her part) threatens to become public knowledge. The princess gazes upon the husband, so distraught by his wife's death, and knows that surely he could never wish his beloved wife harm. Except it was him. And I did not realise when I decided this that everyone suspects the husband first. He has an alibi (he gives her a poison that takes five hours to kill her and had been with the heroine's parents at the time of her death), but I feel like the readers, nowhere near as naïve as our young heroine, will know instantly that the alibi will collapse and he will be revealed to be the killer, especially when his wife's infidelity is uncovered. So how can I throw the readers off the husband and not have them be disappointed when he's exposed ("OK, so it's probably the husband, oh, so it's not the husband, oh, turns out it was the husband, which way am I supposed to be looking?"), or should I just make someone else the killer? I had someone who was blackmailing her who has just lost her advantage, but I wanted to use her as a red herring. I'm very confused and I can't continue with my notes until I know where I'm going. Sorry if this seems a bit incomprehensible or I forgot to mention something important, it's very late at night. Thanks for your help.