The sentence notes that certain people "did not understand the plot's details," and they are the ones questioning the plan for the missing word.  This means the correct answer needs to show the plan's effectiveness or workability, the definition of "efficacy."

The sentence notes the subject has "little experience" in the field, and that this causes the perception described by the missing word. The correct answer needs to demonstrate this inexperience and messing with the established colleagues. "Dilletante," meaning someone who dabbles or an amateur, is the best choice among the answers.

The sentence notes that the subject "outplayed many experienced members." This indicates the missing word means not experienced. "Neophyte," meaning a beginner or a new convert, is the best choice among the answers.

The sentence specifically notes the missing word is "joyous." The sentence also contrasts the missing word with its intended "somber" tone. "Panegyric," meaning a praising and laudatory speech, is the best choice anong the answers.

The boy in the sentence received a "large cut" due to the missing word being on the glass. This means the correct answer will indicate something sharp and able to cut a hand. "Serration," meaning a jagged edge, is the best choice among the answers.

The sentence notes the "straight A student" got a "poor test score." The correct answer must therefore indicate the fact this score was unexpected. "Aberration," meaning a deviation from the normal, is the best choice among the answer.

The sentence contrasts the fact the "posse" knew he was "quite scared," with the "brave" missing word. The correct answer must indicate an appearance or look of bravery. "Facade," meaning the front facing of a building, here used metaphorically, is the best choice among the answers.

The sentence notes that "different groups" came together against the government. The correct answer needs to indicate a unification. "Monolith," meaning a united force or singular front, is the best choice among the answers.

The "hopeful members of the political party" are seeing earlier successes in this new campaign.  This means the correct answer will show they see the earlier campaigns are a model. "Analogue," meaning something similar or a corresponding happenstance, is the best choice among the answers.

The sentence notes the coach has made a "return from retirement," which is necessarily at the end of his "distinguished career." The correct answer will indicate an extra part of his career. "Coda," meaning the last part of a musical work, and used generally to mean a finale, is the best choice among the answers.