Answer:
unfaithful
Step-by-step explanation:
Using the Thesaurus, the word that best replaces the underlined word without changing the overall meaning of the sentence is unfaithful.
The above answer is the correct answer.
This is because looking at the sentence, we discover that the captain confronting the crewmembers is the leader of the team. So, if he is questioning their treacherous behavior, it then means he is questioning their unfaithful behavior.
What leaders look out that their followers or subordinate will be faithful. But when they misbehave, then they start acting unfaithfully.