Suspecting that she's been lying to them, the kids use Mr. Smith to track where Sarah Jane is spending her time. They discover that she's been dating, and she wants him to meet Luke, but doesn't want Peter, her boyfriend to know anything about their work. To help protect Sarah Jane from discovery, Rani takes a box to her house, a box which contains a slug-like alien. The alien escapes while Sarah Jane, Peter and Luke are at dinner, but Mr. Smith transmits the alien back to his homeworld.
A couple days later, while digging around on the internet, Clyde discovers that the house in which Peter claims to live is closed up and listed for sale. Clyde and Rani go to explore the house, while at lunch Peter proposes to Sarah Jane, who accepts. Clyde and Rani fill in Sarah Jane, but the ring which Peter gave her flashes and Sarah Jane seems to come up with a perfect explanation. The ring then forces Sarah Jane to shut down Mr. Smith just as he detects a problem with it.
Two weeks later, it's the big day. But noticeably absent is the Doctor, the sound of whose TARDIS has been heard repeatedly thoughout the events. As the the wedding vows are read, the Doctor runs in, demanding that the wedding stop. A wind kicks up, and the Trickster (from last series' The Temptation of Sarah Jane Smith) appears and steals away Peter and Sarah Jane.
The kids awaken from the Trickster's appearance and disappearance to discover that the entire church has been pulled out of time and that they and the Doctor are the only ones who can save everyone. They run out to to get into the TARDIS only to discover that it's been left behind like everyone else and it can't break through the temporal barrier the Trickster has thrown up.
Meanwhile, Sarah Jane awakens to discover her situation and realizes that the ring is to blame. The Doctor and the kids, in another "version" of the church, try to find her. The Doctor realizes that they are trapped in separate ticks of the clock. Elsewhen, Peter tells Sarah Jane how the Trickster saved his life and extracted a promise to help trap her, and she fills him in on her life. She calls the Trickster out, and he explains to her that all he wanted was for her to settle down with Peter, so that she would give up her life of intervening in the Trickster's plans. Trickster tells her that the only way to save the Doctor and the kids is to marry Peter.
The Doctor attempts to connect to Sarah Jane's clock-tick, which attracts the Trickster's attention. After a battle of words with the Doctor, the Trickster fades again, but the Doctor has his plan all figured out. The TARDIS manages to materialize the doorway, and the Doctor enters but Clyde gets caught in its temporal field. Clyde discovers he is charged with temporal energy, and K-9 explains that the energy could be used to fight the Trickster.
Clyde calls out the Trickster, and manages to hit him with that energy. While Clyde is distracting the Trickster, the Doctor manages to bring the TARDIS to Sarah Jane, who has to decide whether to marry Peter and condemn the world to the Trickster's power, or to say no and be forced to stay in the rift. Before making the decision, Clyde's energy runs out, and the Doctor is forced away. Sarah Jane convinces Peter to rescind his agreement with the Trickster, which means giving up his own life for hers. Everything returns to normal, with all the guests questioning where the groom has disappeared to, and Sarah Jane has to cancel the wedding. Later, at Sarah Jane's house, the Doctor reappears. After showing the kids around, the Doctor and Sarah Jane say their final goodbyes.
I love this show, both because it's well-written, but also because it is simple without being simplistic. Yes, the plot points are pretty obvious, and you always know where the story is going to go, except for those times you don't, and those times are wonderfully done. Yes, I have a particular fondness for Sarah Jane, since she was the first companion I watched. Yes, it's supposedly a childrens' show, but don't let that stop you. It is a spin-off of Doctor Who, but you don't need to know anything about that show in order to enjoy this one. It's great that we got to see the Doctor again; his specials are too separated right now. An enjoyable story all around and a highly recommended series.