The Assassin and the Ranger

I was told this story as an earnest, cherished example of how awesome secrets between players can be in campaigns.

In a high-level AD&D campaign, there was a hapless ranger who was constantly getting killed and being resurrected at great expense. Mostly to himself, I believe--he was deeply in debt to an order of clerics, at a time when the other PCs were getting rich and building strongholds.

For some reason, this irritated another PC, an assassin. I'm not sure if it irritated the PC, or the player.

At any rate, the assassin player approached the GM, saying he wanted to assassinate the ranger. The ranger had no more money available, so this would be his final death.

The GM and assassin player had an impromptu, one-on-one session where the assassin described his plans for finding the ranger in town once the next adventure was over, and how he would go about trying to kill him when his guard was down.  The ranger was a creature of habit

The GM dug up the ranger's stats, and they duelled it out in a hypothetical street ambush - the assassin PC played by his player, and the GM played the ranger, with the GM throwing a few curveballs to try to understand the assassin's backup plans. The mock fight ends with the ranger dead. Satisfied with his plan, the assassin ends his private session.

Time passes. During the group's next session they return to town, at which time the ranger heads off to his usual haunts, exactly as the assassin predicted.

The GM suddenly declares to the ranger that he's under attack by a masked assailant! Using the strategies the assassin described during the rehearsal fight, the GM plays the assassin as an NPC.

The ranger is dumbfounded - who is this guy? Why is he attacking me? His questions are never answered: the fight goes as expected, and the ranger is dead. As far as the player can tell, a high-powered NPC came out of nowhere and killed his veteran PC, for no reason.

With no more cash to his name and too indebted to them already for the church to take pity, it's his final death.

* * *

Other than the fact that the ranger player doesn't know what happened to this day, that's all I know. Still, I have many questions.

Does this sound awesome or awful to you?

Do you think the ranger player had fun?

Does it matter if the ranger player knew it was potentially a competitive game between players?

Did the assassin player get an "extra turn"?

Is it okay that the ranger player still doesn't know what went down?

Is there a meaningful boundary between the game and the players' relationships?