If you haven't seen The Dark Knight Rises, you might want to bookmark this article, and come back later. There will be spoilers.
I have an idea. I know Christopher Nolan is supposedly done with his Batman trilogy. He also clearly set up the idea of where his Robin originates. Below is an idea of where a spin-off film could go. This idea picks up immediately after The Dark Knight Rises ends.
Batman's Robin
John Blake discovers the Bat Cave. Alfred is traveling the world. Commissioner Gordon retires, attempting to repair his relation with his family in Cleveland. Bruce Wayne and Selina are out of the picture. Foley is now in charge of the police. That's right, he was wearing a bullet-proof jacket and didn't die. Long live Modine!
Gotham hails Batman as their fallen hero. He is an untouchable icon who saved everyone. John takes a position helping run the boy's home in Wayne Manor. This gives him access to what really matters, and he's terribly excited to figure the ins and outs of the Bat cave, but has no one to show him the way. Batman's costume doesn't even fit. He keeps thinking of what Batman/Bruce told him about protecting those around him, but also realizes he needs to have people who he can call his family.
John spends a lot of time working with the orphaned boys. There is one boy who is particularly troubled named Barney. Constantly picked on, he's an extremely bright teenage boy, great with electronics, but has a dark side that John doesn't see. John only sees someone he can save. The city of Gotham is attempting to pull themselves together, and leading that charge is a group of white businessmen led by Kyle Vander. Kyle has taken to calling this group of men The Jury. The Jury constantly talks about the way things used to be. They have their hands in everything, including crime.
At a charity function John meets Kyle, as well as the fetching Eva. She's a Green Peace advocate, trying to influence Gotham going green in their rebuilding process. Both John and Kyle are drawn to her. John gets suspicion of The Jury's activities and puts on the Bat suit one night to get a closer look. He's clumsy, barely knows how to use the gadgets, and gets spotted making an escape. The news talks about a Batman sighting. John is trying to file down the bat ears on the costume; he also sheds the cape. He's interrupted when Fox comes to the mansion looking for answers. Barney is curious, but doesn't seem to learn anything from Fox's visit. John however convinces Fox that he has Batman's blessing to carry the mantel, but he needs his own identity. Fox is clearly happy to make some modifications.
Now as Robin, John starts to learn more about The Jury and doesn't like what he's finding. These businessmen are constantly talking about the fondness and control their forefathers had. They are also purchasing large amounts of the poorest areas of Gotham. Many crimes are going unreported and unnoticed by the affluent, leaving the poor to fend for themselves. Fox has a sudden stroke and can no longer help John. News of Batman's re-emergence, and the health of Fox, brings Alfred back to town. Alfred talks to John about the importance of having people in your life. That's what he always wanted for Bruce, and he can see John needs it as well. John takes Alfred's words to heart, but is also getting a little sick of constantly being compared to Bruce/Batman. John makes a date with Eva, only to have it get awkward when Kyle attempts to swoop in and steal his thunder.
While he has plenty of street-smarts and passion, John doesn't have a head for the electronics. He takes further interest in Barney and decides to give him a couple of tests. Barney passes with flying colors and John decides to bring Barney into the Bat Cave, concealing his identity, and making sure not to let Barney know where they are. Every time they go to the Bat Cave, it's an elaborate trip that makes Barney believe it is miles away. While John wants to trust him, he still doesn't know if he can. They form a fantastic team, and Robin starts to fully understand what The Jury is up to. Barney is the sidekick that Robin never was able to be for Batman. Barney is able to make creative devices, deadly weapons and even make modifications to some of Batman's favorite toys, like the Batpod. Now they are the perfect fit for Robin. Robin insists, just like Batman, that the plan is not to kill.
Robin is finally making a name for himself with the city of Gotham, like the Foo Fighters were able to after Nirvana. With Barney's help, Robin discovers The Jury's ultimate plan; eliminate the poor. The Jury talks about it like it's a corporate takeover, but it's much more sinister. The plan is to release a deadly virus within the slums, then declare the areas must be quarantined. Once that occurs, they simply plan on letting the people die. Robin tells Barney that he's coming with to stop the plan in the Gotham slums. Barney doesn't seem thrilled at the chance, and Robin thinks it must be nerves.
Once in the Gotham slums, Barney says they'll be able to cover more ground if they split up. Robin agrees. Even though The Jury has sent one of their members, and plenty of henchmen, Robin is able to save the day. He feels he's able to restore order to Gotham.
Once Robin gets out of his costume, and back to Wayne Manor, there is Alfred, in the main office, dying. John runs to him, but it's too late, Alfred's lost too much blood. "He's got Eva. I didn't tell him anything. I'm so, so sorry," are Alfred's dying words. John calls Barney, and tells him he's heading to Kyle's mansion, convinced he's behind it. Barney sounds worried, and says he'll meet him there.
Robin storms into Kyle's home, screaming for him. Kyle comes down the stairs, alone. Robin demands Eva, but Kyle doesn't have a clue what he's talking about. Instead, Kyle is furious about Robin spoiling The Jury's plan. Suddenly, Kyle drops dead. John turns to see Barney. Barney brags about the fact that Robin couldn't even see how Kyle just died. Clearly, this is one of Barney's creative weapons. Robin also notices a body bag next to Barney. Robin is completely confused.
"Sorry, sometimes I can be a bit of a head case. Do you not understand what's going on?"
He unzips the bag, and Eva's inside, unconscious. Barney goes on the explain that he killed the remaining members of The Jury, knows that John is Robin, poisoned Fox to get close to John, killed Alfred, and only wants one thing ... the location of the Bat Cave. Barney wants his toys. He is also convinced Batman and Robin's type of justice doesn't have a place in today's world. Barney wants to be the hero who kills. He doesn't understand how John can allow evil to live on. He explains that if John doesn't tell him, Eva dies. It's already a given that Barney will kill John. Barney says he's infected Eva with the same toxin used to infect the Gotham slums, and he'll give her the antidote after he's shown him the Bat Cave.
Once outside the Bat Cave, Barney feels foolish to realize it was underneath Wayne Manor the entire time. John starts to get Barney talking about why Barney's done all of these awful things. Barney talks vaguely about medical experiments that were done to him while in an orphanage. He's convinced those experiments left him smarter, but truly scarred. This is the story of Headcase. Awful scientific experiments done to a child that left him gifted, but also on the cliff of insanity. John wasn't interested in the story, but was just buying time to figure out a plan. Without Barney noticing, John pulls out one of Barney's evil creations from just underneath the waterfall. It was one that Barney thought was destroyed, and John shoots Barney with it, wounding him. They battle, but John is able to gain the upper hand. He demands the antidote for Eva, or he'll kill Barney. Even Barney sees that's illogical. Barney charges, John counters, which accidentally sends Barney over the waterfall, clearly killing him on the rocks.
John rushes Eva to a hospital. He explains she's been poisoned. He nervously waits. A doctor comes out to explain they found nothing in her system, she'll be fine. It was all a bluff by Barney, the head case. He walks away.
"Don't you want to be here when she wakes up?"
John leaves, knowing he must be alone, just like Batman, to truly be the symbol for Gotham.
Further Thoughts: Headcase (Barney), and The Jury are characters from the comic books. Eva could become Poison Ivy in a sequel. I don't explain the weapons and gadgets. Feel free to fill those details in. I love the title because Batman creates Robin, Robin lives in the shadows of the iconic Batman, and then this film would rest alphabetically next to Batman.