Season 3 episode 9 of The Flash is titled The Present and it will witness a tense moment between Barry and Wally when the latter reveals that he has been training with HR to help take down Alchemy and Savitar.
The episode will be a Christmas special and it will also focus on Barry's relationship with Iris.
Meanwhile, promo materials from the upcoming episode show the return of Mark Hamill as The Trickster, who looks similar to DC supervillain The Joker. Hamill's character is listed as James Jesse, and it can be safely assumed that he is the Earth-3 version of The Trickster.
The official synopsis of The Present reads: With Alchemy and Savitar still looming threats, Barry (Grant Gustin) is unable to focus on the Christmas holiday, and especially his relationship with Iris (Candice Patton). Determined to stop Savitar, Barry goes to Earth-3 to get advice from Jay Garrick (guest star John Wesley Shipp). Wally (Keiynan Lonsdale) wants to help Barry fight Savitar and reveals that he's been training with H.R. (Tom Cavanagh), which doesn't go over well with Barry. As Cisco (Carlos Valdes) faces his first Christmas without his brother Dante (guest star Nicholas Gonzalez), old wounds are reopened.
Meanwhile, this Tuesday's episode of The Flash was the first part of the network's highly anticipated Invasion crossover and it saw Supergirl meeting several other superheroes including the members of Team Flash, the heroes of Arrow and Legends of Tomorrow. Sadly, all of them got abducted by the aliens called Dominators before the end of the hour.
What happens to them will be explored in Wednesday's Arrow, which is part two of the Invasion crossover.
The Flash airs Tuesdays on CW.