In the table below, the line is colored green if both "fear" and "secret works" are mentioned together and red if "secret works" is mentioned without "fear." Notice which author consistently connects these two concepts.
It is interesting to note how the concept of "fear" gets worked into the text in a variety of contexts when Mormon mentions the secret works, as if he does this on purpose to teach us to connect these secret works with fear:
In Helaman 2, Gadianton fears when Kishkumen did not return from a planned secret murder of Helaman, the chief judge.
In Helaman 8, the corrupt judges feared the people who seemed to be believing the words of Nephi. They were compelled because of their fear not to lay their hands on him.
In Helaman 10, a voice comforts Nephi as he is "much cast down" while pondering the secret works of darkness of the people. The voice tells him he is "blessed" because he "[has] not feared them."
In Helaman 11, the growing numbers of the robbers were able to "defy the whole armies of the Nephites, and also of the Lamanites." This caused "great fear to come unto the people."
In 3 Nephi 3, the people face a serious threat from the robbers. Their righteous leader Lachoneus "could not be frightened by ... a robber." He tells the people what they must do in order to stay safe. His "words and prophecies" caused fear to come upon the people. They feared his words. (Later in 3 Nephi 4, when the robbers come to battle against these righteous, prepared Nephites, this happens:
8 And it came to pass that the armies of the Nephites, when they saw the appearance of the army of Giddianhi, had all fallen to the earth, and did lift their cries to the Lord their God, that he would spare them and deliver them out of the hands of their enemies.
9 And it came to pass that when the armies of Giddianhi saw this they began to shout with a loud voice, because of their joy, for they had supposed that the Nephites had fallen with fear because of the terror of their armies.
10 But in this thing they were disappointed, for the Nephites did not fear them; but they did fear their God and did supplicate him for protection; therefore, when the armies of Giddianhi did rush upon them they were prepared to meet them; yea, in the strength of the Lord they did receive them. (3 Nephi 4)
This is a very interesting spectrum of treatments of the words fear. We learn several important lessons, right up to the most important lesson -- we should fear God, not man, and certainly not secret works of darkness.