Batman stared intently at the little brick building by the river. It clearly wasn't big enough to be a headquarters for the Riddler, so there was really only two explanations for it. It had an underground portion, or it was a trap. Batman decided it was more prudent to temporarily assume that the latter was the case, and glided down to the door. He hid behind it as he pulled it open, but nothing happened. He walked in. Wherever he was, it had clearly been designed by the Riddler. Almost every surface in the room was either green or illuminated by green lights, and purple question marks were scattered about. Judging by the approximate dimensions of the room, it took up roughly half the building. There were two screens, one showed a hostage suspended over something off-screen. The other, was a blank green background with another purple question mark. There was a large iron door cutting Batman off from the rest of the building. The Riddler's voice echoed through the chamber.
"So. The world's greatest detective challenges the world's greatest criminal once again."
Batman looked around, and saw that he had appeared on the unoccupied screen.
"Or at least the most egotistical one."
"Careful, Dark Knight. I have a hostage."
He held up a button and put his finger to it, but didn't push.
"But I'll be sporting."
"What's your game this time, Nigma?"
"Now, now, Batman. You sound almost impatient. If you must know, I think I'll be playing some solitaire while you puzzle your way through my conundrums. Speaking of which, I have three riddles for you. Each right answer will raise this poor fellow away from the acid. Each wrong one will lower him an equal distance. Right now, if he drops any lower, he'll be going for a swim. Choose your answer carefully. We'll start off with a simple one. I am the enemy of all. Many have evaded me, none have escaped me. I cannot be stopped, I cannot be bargained with. What am I?"
Batman thought for a moment, before deciding on an answer.
"Death."
For a moment, no answer came. A chill went down his spine as he thought for a moment that he had doomed the hostage with his answer.
"Very good, Dark Knight! And by answering as such, you prolong our friend's life."
The hostage was pulled up several feet. Batman heard a clicking sound from underneath the iron door.
"There are two riddles yet. Shall we try the next? Roses are red, and Violets are blue, Teardrops are cyan, what color are you?"
Batman's first reaction was that this involved color, as teardrops are unrelated to roses and violets. Riddler had mentioned red blue, and cyan. Red and blue are both primary colors for both light and pigments. Cyan is not. Cyan is a mixture of blue and green, the third primary color for light.
"Green."
"Interesting answer. The correct one is 'Blue.'"
The hostage slid back down to his starting position. Batman clenched his fists.
"Blue? Why blue?"
The Riddler's face adopted a wicked grin.
"That would be telling*. Now, the third puzzle. This is the hardest, so I regret to say that there is not much hope for our mutual acquaintance."
"Just tell me the riddle, Nigma."
"Very well. How can you add ten to ten and still have ten?"
Batman considered this for several minutes. He began to think he had to give it up, but he knew he couldn't. He began looking for ways to bypass the door while still thinking about the riddle. He looked down at his fingers and the answer dawned on him.
"Gloves**."
The hostage was dragged upward again. Batman heard two more clicking noises from beneath the door as it slid open. The Riddler jumped up in surprise.
"What? How did you-"
"It was a bad idea coming here in person."
"I don't have bad ideas, Batman."
Something landed on the roof.
"I have back-up plans."
Firefly crashed through the window.
"Mr. Lynns, if you please?"
"With pleasure, boss. Just remember the paycheck."
"I will."
Firefly turned to Batman as the Riddler exited through another door.
"You're playing with fire, Bat. I think it's about time you got burned."
He turned his flamethrower on the hostage, but didn't have the chance to attack. Batman grabbed the flamethrower and threw it on the ground. Firefly tried to punch him, but he blocked it and ripped his helmet off. Firefly jumped backward and tried to retrieve his flamethrower, only to receive a knee to the stomach.
"Gah! You're dead, Bat-freak!"
Batman punched him once in the head, knocking him out.
"Not likely."
He fired his grapnel gun, pulling the hostage clear of the vat of acid, and then threw a batarang to get him down. Batman chased after the Riddler before the hostage had a chance to thank him. Batman ran out onto a small dock, and found nothing. The Riddler was gone. He turned on his communicator.
"Alfred, I'm coming back."
*This is a reference to the "Am I Blue" scene from Justice League Unlimited. I don't remember the episode title, but it's the one where Wonder Woman gets turned into a pig.
**This is also a reference to something. It could be interesting to see if anyone gets it, since it's pretty obscure.