Which word best describes the narrator based on this excerpt I had a different suspicion darker one that dared not voice but it decided my course of action would proceed with experiment.?

Based on the excerpt, the word that best describes the narrator is suspicious.

Here's why:

* "I had a different suspicion, a darker one": This clearly indicates the narrator is harboring a suspicion, and it's not a casual or light one.

* "that dared not voice": This suggests the suspicion is strong but the narrator is hesitant to express it openly. It implies a fear of being wrong or facing consequences.

* "but it decided my course of action": This shows the suspicion is powerful enough to influence the narrator's actions.

While the excerpt doesn't provide enough information to say the narrator is paranoid or secretive, the focus on the suspicion and its influence on their actions make "suspicious" the most fitting word.