Ep 15. The Fifth Halliwheel

In the Charmed season 4 episode 15 titled "The Fifth Halliwheel," we see the Charmed Ones being visited by a young woman named Chris who claims to be their half sister. Chris informs the sisters that their mother, Patty, had an affair with a Whitelighter named Sam, which resulted in Chris's birth. The sisters are taken aback by this revelation, and they decide to investigate further to authenticate Chris's claim. Meanwhile, Leo is suspicious of Chris's intentions and worries that she may be working for the Evil Forces.

As the sisters delve deeper into their investigation, they discover that Chris has a mission of her own. Chris comes from a future where the Charmed Ones have been wiped out, and she has traveled back in time to prevent that from happening. Chris, along with Leo, had been spying on the sisters to determine if any of them are potentially the weak link that leads to their downfall. Chris's suspicion falls on Phoebe, who has been going through a tough time in her marriage.

Feeling scared and alone, Phoebe turns to Cole for comfort. Cole, who is secretly working as an agent of the Evil Forces, takes advantage of Phoebe's vulnerability and tries to convince her to leave her sisters and start a new life with him. However, Phoebe remains conflicted and unsure of what to do. Meanwhile, the sisters and Leo race against time to prevent a demon from killing a witch who holds the key to stopping the Evil Forces from destroying the Charmed Ones.

As the sisters and Leo work together, they start to trust Chris and begin to see her as not just a sister, but as an ally. They realize that they need all the help they can get to prevent the Evil Forces from destroying them. With Chris's help, they successfully save the good witch and thwart the demon's plan. In the end, the sisters embrace Chris as a part of their family, and they vow to stand by each other no matter what.

"The Fifth Halliwheel" is an emotional episode that explores the themes of family, trust, and betrayal. Through the introduction of Chris, we get to see a different side of the Charmed Ones and witness their vulnerability as they come to terms with their mother's affair. The episode also delves into the dynamics of Phoebe and Cole's relationship, which has been on shaky ground for some time. Overall, "The Fifth Halliwheel" is a captivating episode that leaves the audience eagerly anticipating what's in store for the sisters in the future.