Warning: Spoilers ahead for Doctor Who season 14, episode 7, "The Legend of Ruby Sunday."

Summary

• Sutekh has been hiding aboard the TARDIS, causing it to make strained noises.
• Ncuti Gatwa's Fifteenth Doctor faces the formidable power of Sutekh, showcasing the god's terrifying abilities.
• The TARDIS' ominous groan reveals Sutekh's integration with the Doctor's ship, marking a dangerous turn in the show.

The One Who Waits was Sutekh the whole time, and his return was foreshadowed by a noise coming from the TARDIS that started during David Tennant's temporary return to the role for the 60th anniversary specials. Sutekh's only previous onscreen appearance came in 1975's "Pyramids of Mars" story, with the god of death facing off against Tom Baker's Fourth Doctor almost half a century ago.

The lore surrounding Sutekh appears to have been retconned slightly, placing him atop Doctor Who's classic era has been hiding in plain sight - right under the Doctor's nose.

The Previous Doctor Who Episodes That Featured The TARDIS Making A Groaning Noise

It all started in "Wild Blue Yonder"

The TARDIS' groaning noise in "The Legend of Ruby Sunday" isn't the first time the Doctor's blue box has sounded strained. The first time the Time Lord's iconic space and time machine lets loose the ominous noise is in "Wild Blue Yonder," when the TARDIS crash lands after Donna Noble's coffee mishap. At the time, the damage to the Doctor's blue box makes the noise seem very understandable, although even David Tennant's Fourteen Doctor describes the sound as "Strange."

The TARDIS didn't repeat the noise until after Ncuti Gatwa had taken the show's reign and stepped into the role of the Fifteenth Doctor.

The TARDIS didn't repeat the noise until after Ncuti Gatwa had taken the show's reign and stepped into the role of the Fifteenth Doctor. In Doctor Who season 14, episode 2, "The Devil's Chord," the Doctor narrowly prevents Jinkx Monsoon's Maestro from hijacking the TARDIS, putting the blue box under great strain. Again, in context, the sound doesn't sound all that suspicious, although the Doctor does seem cautious about its possible cause. So, "The Legend of Ruby Sunday" may be the most prominent instance of the TARDIS' worrying moan, but it isn't the first.

Why The TARDIS Was Groaning In Doctor Who

Sutekh was putting a lot of strain on the blue box

The strongest theory to explain the TARDIS' groaning is that it was directly related to being forced to carry around Sutekh as a enger. The classic era villain is an incredibly powerful being, and it couldn't have been easy for the TARDIS to carry such a lethal figure through time and space. Like the Doctor, the TARDIS was likely unaware that Sutekh was aboard, so although it probably knew something was wrong, it wouldn't have known what it was or how to rectify the problem.

What's currently unclear is exactly how long Sutekh has been integrated with the TARDIS systems. One possibility is that he has been there since Tom Baker's Fourth Doctor trapped Sutekh in "Pyramids of Mars." Four used a piece of the TARDIS to help carry out his plan, so he could have unknowingly bound Sutekh to the TARDIS. Then, the Doctor's ship could have started to feel the strain as The One Who Waits started to stir in "Wild Blue Yonder."

Alternatively, Sutekh may have been able to latch onto the TARDIS when Fourteen and Donna were forced to crash-land on a ship so close to the edge of the universe. The laws of reality are different so far out, and so Sutekth may have been able to reenter the universe and then stow aboard the TARDIS until he was ready to emerge. Either way, Sutekh's presence is more than likely the cause of the TARDIS' fatigue.

What The TARDIS Noise Reveals About Sutekh's Doctor Who Return

Doctor Who has made it clear how powerful Sutekh really is

Sutekh's power can be seen as early as his first franchise appearance in 1975. All it takes is for him to touch a living being, and they turn to dust before him. He can also inhabit sentient, organic beings and make them serve as his avatars, such as Harriet Arbinger and Susan Twist's Susan Triad. Even out of context, his abilities are fearsome, but they're highlighted even more by what he's able to do to the Doctor and his TARDIS.

The TARDIS harbors its own immense power, and it's proven to be too much for certain beings to handle. For example, Rose Tyler almost dies when she looks into the heart of the TARDIS, and it even causes Christopher Eccleston's Ninth Doctor to regenerate. The TARDIS' power doesn't seem to be a hindrance to Sutekh, as the god of death successfully stows away without being harmed. There's also the matter of the Doctor being duped for an extended period of time, making Sutekh an even rarer breed of villain in Doctor Who lore.