When we left the Doctor at the end of Series 3, he had averted a time paradox disaster and held his arch-enemy, the Master, as he died in his arms. Oh, and Martha left him, and Jack declined to leave Torchwood to travel with him. As we've learned previously, leaving the Doctor alone is never a good thing.

By Juli Monroe

The closing scene of series 3 shows the Titanic crashing into the TARDIS. That's the lead-up to the Christmas Special, but you need to pause and track down a video on YouTube before you watch the special.

"Time Crash" is a short adventure produced for the Children in Need event. It's worth watching because it shows the Tenth Doctor meeting the Fifth Doctor. Anything else would be a spoiler, but it's a fun 8-minute video. It's even more fun when you realize that the Fifth Doctor is David Tennant's favorite. Share the fan boy moment.

Now you're ready for the Christmas Special, "Voyage of the Damned." Previous incarnations of the Doctor have been ready to jump in to save the Earth, Universe or whatever. Events can touch his emotions, but he usually stays at least a bit detached from the pain and devastation around him. Not Ten, and we see it strongly in this special.

Some people die in this special, and it damages him. He's not completely whole in this series, or beyond. This is going to become important after this series, in the specials that bridge the gap between this and Series 5. As always, he survives and moves on, leaving the events behind but still holding them in his heart.

Fortunately, he doesn't go long without a new companion. Back on Earth, he reunites with Donna Noble (remember her from "The Runaway Bride?") Their reunion scene in "Partners in Crime" is one of the funniest in the entire show. Catherine Tate is an excellent comedic actress, and she demonstrates it beautifully in this scene.

Donna and the Doctor have an excellent relationship, but it's different from his relationship with either Rose or Martha. He makes it clear in the beginning that he's looking for a mate (friend). Of course, there's an hilarious bit where Donna interpretes that to mean he's looking for a mate (breeding partner). Although plenty of fanfiction postulates a romantic relationship between them, they really are just good friends. Donna is more mature than his previous companions, and she doens't hesitate to challenge him when she thinks he's going too far. There's an excellent example of this in "The Fires of Pompeii."

Two of the best episodes in series 4 are "Silence in the Library" and "Forest of the Dead," written by Steven Moffat, current showrunner for the Eleventh Doctor. These two episodes introduce the character of River Song (Alex Kingston), who will become important to the Eleventh Doctor.

Martha Jones comes back for several episodes, and we see more fun interplay between two Doctor companions. The series culminates in an exciting two-part arc which brings back another old companion. I won't spoil it for you.

Unfortunately, the Doctor is again alone at the end of this Series, and that's going to greatly impact the four specials to come.