This is similiar to other's suggestions:

1. Boss 1 dies with his war party. One party member escapes to hide in the cave and becomes Boss 2.

2. Boss 2, being a member of the war party and working for Boss 3, begs for his life in return to passing on his knowledge of Boss 3. This could make an interesting choice where the player can kill him after he has shared his news.

3. Boss 3, the head of all of these miscreants is in his castle awaiting word of Boss 1's recent raids. Disguised as Boss 1, the player enters and confronts Boss 3. (Be sure to give the player a disguise item after he kills Boss 1.)

Hope these get your juices sparked. :)

What about:

Boss 1 is intending to pull a "Benedict Arnold" (Can you believe he's still remembered as a traitor?) And he takes Dwayne's (Boss 3) loyalists to suicide rush the enemy, then he pretends to be dead on the battlefield. When the smoke is clearing the PC(s) finds him trying to sneak away to a cave (!) and they have the boss fight.


Boss 2, who is then jumpy because Dwayne is probably going to kill him soon, mistakes PC as member of a raid and they fight to the death. Ultimately realizing that PC is on his side, Boss 2 gladly tells where Dwayne is, hoping he dies like the dirty dirty dog, Boss 2 takes him to be.


Dwayne lets PC enter after hearing that PC's kind of...routed the defectors which, technically would have been on the side they were fighting for--but at least it proves to Dwayne that they're on his side, because no one would just kill their own people like that...

Rather than letting the player know where Boss 2 is after fighting Boss 1, why not let the player know while on the way to fighting Boss 1? To me, it would seem a bit more natural (or at least a bit more like something from Deus Ex). That way it gives the player a bit more motivation to fight Boss 1. I picture something like the following:

(Hero and his party are on the way to fight Boss 1, who is a known criminal/warlord/pumpkin stealer)
Party Member: Oh, look! I just recieved a transmission from Joe back at headquarters! He says he knows the whereabouts of Boss 2, and said to swing by HQ after we are finished with Boss 1!
Player: Okays! Lets go beat Boss 1, then go to HQ to find out where Boss 2 is!
(and with that they prance on their merry way to Boss 1)

Sorry, I got a little carried away there...

Firstly, let me just say I love your question! I'm hoping once my game is ready for this level of problem, I'll have a good solution in hand.

I agree with a few of the comments here that if at the end of each boss fight, you get a note/dialog/message that tells you which boss to go and kill the next boss, it can really make the game feel repetitive (go through minions -> kill boss -> rinse and repeat).

One solution is (as a few people have suggested) make it a little less linear. Give some choice. Allow the player to go to places out of order, to explore dead ends, to bypass places/bosses completely. These kinds of games (e.g. Wastelands/Fallout) are an absolute joy to play when done right, but they're very hard to do right and it's easy to leave the player feeling lost. For us indies, this is a big ask.

Another solution is to keep the linearity, but to mix up the way you guide the player through it. Instead of saying "now go here and kill this boss", say "I've got to stop that train!" or "I need to rescue that P.O.W to get more intell", or "I need to destroy that research facility". The fact that there is a boss waiting for you somewhere in all of these tasks doesn't take away from the player's feeling that they're achieving different objectives. And given the objectives now relate to the story, there are lots of options as to how these get delivered (e.g. player's inner voice, headquarters, NPCs, etc) - indeed you can use them to construct the story, rather than just fit into it.

The final option that springs to mind is to totally embrace this in your story. For example, if your player is a cop, it makes sense that dispatch will send you a series of "kill/stop" dude X objectives.