Disclaimer: I don't own Young Justice.
Robin's POV: I am at Gotham and decide to walk to the house. From there, I can get to the Batcave. I decided to walk. Saw a robbery along the way. Stopped them before they could get away. Then I came across Barbra, no doubt that she was looking for Dick Grayson, not Robin. I doubt she knows my identity. So I walk past her without a word. I then walkover to the mansion. I go ahead and change into plain clothes. I throw my sunglasses on and head to the Batcave. The moment I step into the batcave, the whole group turn on the lights and say, "Surprise." They trap me in here. There is no way out of this one, unless...Ah ha! My escape! I use my smoke bomb and then I use my grappling hook and and aim it at the escape vent that the Bat put in. I shoot it only to find out that they blocked it off. No point in trying anymore. My master already knows. Someone spills water on me. Gets into my circuits. Malfunctioning.
Meanwhile, at the Cave: Hahahahaha... It works, they now know that I am not at their party. Now I radio Zatanna, "Come to the cave." She comes over and we have a good time. This has been the best birthday ever.