WARNING: The following contains spoilers for DC's Legends of Tomorrow Season 6, Episode 10, "Bad Blood," which aired Sunday on The CW.
John Constantine is well known throughout the world as a Master of the Dark Arts, but during a mission on Legends of Tomorrow, he was stripped of his connection to the magical realm when he saved the team from Aleister Crowley. And after failing to progress fast enough during lessons with Astra, John went out in search of the Fountain of Imperium. Now, in "Bad Blood," John finds the fountain, only for the cost to be higher than anyone anticipated.
After learning from Gary that the map to the Fountain belongs to Crowley, John heads back to his home to question the painting. He quickly threatens him with gum and bodily fluids, and Crowley gives in and tells John he entrusted the map to a banker, Noelle, who arrives at John's door and stands by, awaiting an invitation. John realizes she's a vampire and gives her permission to enter, but she demands two million quid for the map. John makes a counteroffer, though, so Noelle attacks him and lands herself in a trap. She then gives John the map and leaves him a potion she procured for Crowley that might come in handy.
With the map, John narrows down the location to Spain, and with Spooner's help translating the alien artifact, tracks it to the city of Albacete in 1939. The pair take off in the jump ship and set course, hoping to find the fountain at last. John believes there was a man named El Gato who might've drunk from the fountain because he was rumored to have survived seven assassination attempts. They make their way to a bar to gain some intel, only to discover a mute child named Fernando, who Spooner communicates with telepathically. But before they can get any real information, soldiers rush into the bar and demand El Gato lead them to the fountain. They shot a bar patron, leading Fernando to resurrect him, proving that he was the one who used the fountain. So, as Spooner, Fernando and the bar patrons are trapped inside, John comes up with a plan to dress up a priest and fool the soldiers into allowing him to gain Fernando's trust. And while it works at first, it results in a shootout that gives John, Spooner and Fernando an opportunity to escape.
Fernando leads them to the Fountain of Imperium, which has unfortunately dried up, but a desperate Constantine isn't ready to give up. He theorizes that Spooner could transfer Fernando's magic into him, freeing the boy from a life of magic. Fernando agrees to this in exchange for John finding his mother. But as the transfer begins, Fernando's magic foes past John into the fountain. And before John can even react, the trio was ambushed by the soldiers. Thankfully, John manages to get Spooner and Fernando out, but he's left with only one option -- drinking Crowley's potion.
Once John drinks the potion, he's sent into a psychedelic trip where his connection to the magical realm is overpowered, allowing him to take down the soldiers without any trouble. Unfortunately, the trip doesn't last long and John is quickly returned to his depowered state, greeted by a horrified Spooner. After returning to John's house, drunk from the celebration, Spooner urges John to tell her what was in the potion. Unwilling to answer, John licks the potion's cap, giving him a touch more magic, which he uses to hypnotize Spooner into believing the mission was a success. Once upstairs, Crowley judges Constantine for drinking the potion, knowing the addictive dangers of it. But John is too far gone, and soon, Noelle enters his home and trades six more vials of the potion for Crowley. The episode ends with John staring at his new, temporary source of power, which may corrupt him in a way he never thought possible.
If John is going to get out of this mess, he'll need the help from his friends on Legends of Tomorrow, which airs Sundays at 8 p.m. ET/PT on The CW.