Ep 17. Flash Back

Barry Allen, aka The Flash, is struggling to get faster in order to beat his nemesis Zoom. At STAR Labs, the team is experimenting with a new drug called Velocity-9 that could enhance Barry’s speed. However, Barry is hesitant to try it as he recalls the detrimental effects of the previous version.

Meanwhile, a blast from the past arrives at STAR Labs - Hartley Rathaway, aka Pied Piper - who was last seen in season one. Hartley claims that he knows how to defeat Zoom and he needs Barry’s help to do it. The team is hesitant to trust him but Barry sees this as a potential way to gain an edge against Zoom, so he decides to go along with Hartley’s plan.

In order to accomplish his objective, Hartley requires Barry’s speed to power a device that will open a portal to Earth-2. While running, Barry experiences a strange sensation and finds himself back in time, a few months before he gained his powers. With the help of Hartley, he sets out to correct past mistakes that he never even knew he made, while trying to keep his identity as Future Barry a secret.

Barry’s experiences in the past bring him face to face with his mentor, Dr. Harrison Wells (the original version) and his team from the first season, including Caitlin Snow and Cisco Ramon. However, they all look completely different in this altered timeline, which leads to some humorous moments. Barry realizes that his actions in the past could have unforeseen consequences on the present timeline.

The episode takes us through a series of familiar set pieces from the first season, albeit with a fresh perspective, as Barry encounters familiar faces and events from a very different angle. However, as he rushes to put things right, he realizes that his meddling is making things worse and he begins to question whether he should try to change the past at all. Many of the main plot points from season one, like the particle accelerator explosion, are addressed from a new angle, which is sure to delight fans of the show.

As the timer ticks down, with Barry’s trip into the past becoming more and more desperate, he realizes the true reason why he was sent back and that not all of the consequences of his trip will be bad. There are plenty of revelations and heart-warming moments that will keep audiences engrossed for the full hour.

The episode is another fine showcase for Grant Gustin’s talents as an actor, giving him the opportunity to explore more of Barry’s character arc. It also allows for some great comedic moments, particularly Cisco's first encounter with his future self, as well as some genuinely moving scenes, particularly a touching moment between Barry and his father.

Overall, "Flash Back" is a great example of the show’s ability to mix humor, heart, and character development, while simultaneously delivering some top-notch action set pieces. It’s also one of the more successful uses of time travel on the series, providing another twist on the famous butterfly effect trope. Fans won’t want to miss this chance to revisit some of the best moments from the show’s early days while also getting some hints about what’s to come in the future.