'Billy and Colin are suddenly in danger of being caught and exposed to the enemy - and each must race to uncover the identity of the other man in time to save themselves. But is either willing to turn on their friends and comrades they've made during their long stints...'
Does this sentence mean that they didn't want to attack their friends they have made?
The complete sentence I found online is
But is either willing to turn on their friends and comrades they've made during their long stints undercover?
This a rhetorical question. It is meant to pique your interest and entice you into watching the film. The implied message is "watch the movie to find out!" In other words, the question does not imply that one, or both, characters turned on each other. On the contrary, it does not reveal any of the characters actions, and you are being encouraged to watch the film to find out what happens.
In this case, turn on likely means betray rather than attack.
A quick Google shows that the quote you've posted is from the plot summary of the movie "The Departed", which adds a little more context.
Billy and Colin are suddenly in danger of being caught and exposed to the enemy - and each must race to uncover the identity of the other man in time to save themselves. But is either willing to turn on their friends and comrades they've made during their long stints undercover?
In English, the idiom 'to turn on someone' means to attack or criticize someone suddenly. For example:
More loosely, it can also mean to sacrifice someone in order to achieve your goals, which fits the context here. The plot summary is stating whether Billy and Colin are willing to sacrifice the friends they've made undercover, in order to find out who the other is.
