For fans of “The Flash,” the wait for the show’s return since Wally West’s (Keiynan Lonsdale) Christmas surprise has been far too long. Happily, the CW series is back Tuesday with its Season 2 midseason premiere episode, “Potential Energy.” However, a lot changed in the big fall finale, as exemplified by that shocking Dr. Wells (Tom Cavanagh) cliff-hanger. So fans may require a little refresher before rejoining Barry (Grant Gustin) and the gang.

It was Christmas on “The Flash” in episode 9, and snow was falling in Central City, even though the forecast was for clear weather. Unfortunately, the weather surprise was not a Christmas miracle but the work of Mark Mardon (Liam McIntyre), aka the Weather Wizard, who whipped up the blizzard to break Leonard Snart (Wentworth Miller), alias Captain Cold, and James Jesse (Mark Hamill), alias the Trickster, out of Iron Heights to kill the Flash.

Of course, Jesse was on board, but Snart, who owed Barry for saving his sister, said, “Thanks, but no thanks.” In fact, Snart even paid a visit to Barry’s house to warn him and Iris (Candice Patton) that the Weather Wizard and the Trickster were after him. Snart also told Barry the reason he did not join Mardon in carrying out the scheme was because there was no money in it.

Speaking of Iris, she finally confessed she had found out Joe had another son, Wally West, this one with Francine (Vanessa Williams). Francine never told Joe (Jesse L. Martin) she was pregnant when she left, so Iris and Barry agreed to tell him together. After hearing the news, the detective feared lying about Francine being dead all these years was not really to protect Iris, but to shield himself from Francine, a decision he feels cost him knowing his son.

Meanwhile, the Weather Wizard and the Trickster were up to no good. Jesse posed as a shopping-mall Santa Claus and gave out wrapped bombs to hundreds of unsuspecting kids, while Mardon lured Barry to the scene. They gave Barry a tough choice: either let them kill him or see all the kids get killed. Barry let Mardon take him down, and Barry took quite a beating as Dr. Wells and Cisco (Carlos Valdes) devised a plan to employ magnetism to use one of the bombs to pull all the others into a portal created by the portal gun. Thankfully, the plan worked.

The Flash Barry (Grant Gustin, pictured) hunts for Mark Mardon (Liam McIntyre, not pictured) in episode 9 of Season 2 of “The Flash.” Photo: The CW

After Barry heard he was in the clear, he made quick work of the two villains, but when Patty (Shantel VanSanten) showed up to make the arrest, she pulled her gun on Mardon instead — Mardon killed her father in a bank robbery years ago.

Patty was considering whether to take justice into her own hands, but Barry (as the Flash) begged her not to do it. He knew all too well that revenge does not heal any wounds. He warned she would distance herself from everybody she cares about should she pull the trigger, and, eventually, Patty chose to reach for her handcuffs.

Afterward, Barry took a cue from Patty’s noble move and decided to attempt to forgive Wells, Earth 1 Wells. Plus, Joe stopped by to admit he was now ready and excited to meet his new son. However, he did give Barry his watch, the gift he always meant to give “to his son.”

As if that was not enough emotion to go around, Jay (Teddy Sears) and Caitlin (Danielle Panabaker) shared an overdue kiss Christmas Eve at Joe’s and Barry’s house. And then, an unexpected visitor showed up, Wally West. At first, he offered to come back at another time, but a shell-shocked Joe and Iris invited him into the house.

However, the biggest surprise came in the episode’s last scene when fans found out why Wells had been so stressed since his cold open encounter with Zoom (Tony Todd). The big bad guy is making Wells an offer he cannot refuse: Help him steal the Flash’s speed and he will let Jesse (Violett Beane), his daughter, live.

“I’ll do it,” Wells promised.

“The Flash” Season 2 returns Jan. 19 with episode 10, “Potential Energy,” and, while Barry may be done with the Trickster for now, the show still has a few tricks up its sleeves. Fans will get a whole lot more of Wally West in the new episode. Plus, the promos have been teasing the arrival of Killer Frost (Panabaker again) and Deathstorm (Robbie Amell) via Caitlin’s and Ronnie’s Earth 2 counterparts. “The Flash” is showing no signs of slowing down.

“The Flash” airs on the CW Tuesdays at 8 p.m. EST. Watch the trailer for “Potential Energy” below: