When you think "White Rabbit," you might not immediately think Gotham, but you will see the Oct. 24 episode, which is titled "Follow the White Rabbit." As you might have guessed, Jervis Tetch is continuing to collect a group of Alice in Wonderland-inspired accomplices, and his latest is the addition of the White Rabbit, a new Gotham character who is dressed in all white to emulate the character. In Lewis Carroll's book, the white rabbit is a messenger who compels Alice to follow him into Wonderland. It's worth noting that there is a DC Comics character called the "White Rabbit," but since she's a villain named for her speed and ability to be in two places at once, not an association with the Mad Hatter (the villain Jervis Tetch is based on), I don't think Gotham is adapting that character.
Tetch is now totally out for revenge on Jim Gordon for keeping him away from his sister and therefore being responsible for her death (in Tetch's twisted mind, at least). His revenge will aim to take something away from Jim that means as much to him as Tetch taking control of his sister's poisonous blood, and somehow, the White Rabbit will be helping him to do it. On Gotham, Tetch usually likes to be his own messenger, telling his victims exactly how helpless they are, so for some reason he must need to send someone a message, be it target Jim Gordon or another person pursuing him (Captain Barnes, Lee, or snooping journalist Valerie Vale, perhaps?).
I'm not sure why someone would want to help Tetch, but his Tweedledee and Tweedledum accomplices don't seem to be hypnotized, so it's possible that the White Rabbit will be a willing helper to the Mad Hatter. But most of the people in Jervis Tetch's orbit are being hypnotized by his powers, so it's also possible that the White Rabbit will be a victim as well, and maybe even used as a pawn in his plans to lure Jim Gordon to his doom. Like the White Rabbit in Alice in Wonderland, this character could be the one who prompts Jim to follow him into "Wonderland," or deliver the rules for what Tetch expects from his victims.
It seems that the White Rabbit will be played by Kieran Mulcare, recently of Jessica Jones, where he played Ruben, Jessica's neighbor who faced a tragic fate and wound up getting dumped in the Hudson River. Judging from the trailers, Mulcare is the man dressed all in white (complete with white hair) that you can spot for a few seconds. If he's an innocent bystander the way Ruben was, hopefully he has a happier ending than on Jessica Jones. Gotham can be grim, but Jim Gordon has managed some pretty impressive saves over the past few seasons. Whether or not the White Rabbit winds up surviving Tetch's plan as either a willing participant or a rescued hostage, it will be exciting to find out exactly what this Mad Hatter has in store for his attempted revenge on Jim Gordon in "White Rabbit."