The Flash season 2 returns with an all-new episode this Tuesday (29 March) at 8pm EST on The CW. In episode 17 titled Flash Back, Barry Allen will travel back in time to meet his nemesis Harrison Wells so that he could teach the speedster to run faster.

The official synopsis for the episode reads as follows:

After the shocking revelation that Zoom is Jay Garrick (Teddy Sears), Barry (Grant Gustin) is more determined than ever to get back to Earth-2 to stop Zoom forever. Desperate to find a way to increase his speed, Barry decides to travel back in time and masquerade as his earlier self in order to get his arch-nemesis, Dr. Harrison Wells/Eobard Thawne (Tom Cavanagh), to teach him how to run faster. However, things don't go as planned and Barry is stunned to face familiar foe Hartley Rathaway (guest star Andy Mientus), as well as old friend Eddie Thawne (guest star Rick Cosnett). Iris (Candice Patton) makes peace with her past in order to embrace her future.

Click here to watch the episode online on The CW website in the US.

In the previous episode of The Flash, Barry and the Star Labs team found out that Jay Garrick was Zoom. In order to defeat the speed demon, Barry will turn to his old mentor Eobard Thawne (who disguised himself as Harrison Wells in season 1 and was killed in season 1 finale episode).

A promo released for the episode shows Barry back in the timeline when Harrison Wells was alive. The trailer opens with Wells hitting Barry in the head and chaining him up. He asks Barry: "Who are you? I mean who are you really?" To which Barry replies: "Dr Wells it's me, Barry." But Wells refuses his explanation and says: "You are from the future."

We also see Eddie Thawne and Piped Piper in the trailer as Barry begins to see the side effects of time travel. Barry fights a time wraith, a ghostly creature which, according to Eobard, comes after someone who has travelled back in time. The promo ends with Cisco, Piper and Caitlin seeing the weird monster as Piper jokes: "Holy Harry Potter." The upcoming episode of The Flash will see time travel get a whole lot scarier.