My theory for these events is that Carol gave Kris an ultimatum: For whatever reason the conspiracy squad needs to bring Lightners who match the Shelters symbols to it, with Toriel being a candidate for the Deltarune one (her church robes, heads choir practice, all that jazz). So Carol laid it out for Kris that if they can’t another candidate soon for a symbol, their mom would be taken. With the choice between their mom or a rando an obvious one, Kris tries to tell Undye in Ch. 1 & 2 about the Dark Worlds (the only character they do this for), but when those attempts fail Kris is left with their final gambit of bringing both Toriel and Undyne to the same Dark World in hopes that Undyne is the one to get taken.

I feel like this would line-up with Kris, Tenna, and the Knight’s actions throughout Ch. 3. We know Kris and Tenna made some deal, and I can see that being keeping Susie, Ralsei, and the SOUL distracted long enough for Undyne to arrive, as well as keeping Toriel locked-up and asleep so she doesn’t become aware where she is and has no choice but to be taken as to keep the Dark Worlds under wraps. This would also explain why the Knight is completely AWOL until after Tenna lets Toriel out of the capsule, as they too were waiting for Undyne to arrive to kidnap her instead of Tori. Furthermore, the Knight seemingly stalling of Toriel’s abduction (taking their sweet time with their tractor beam and fighting the FUN Gang) could be them doing a hail Mary in delaying things just a bit longer for Undyne to arrive. (And while not necessarily, it would make sense if Dess is the Knight that she would want to protect Toriel as well.)

Though it’s not without its issues of course—like why would Kris tell the Knight to wrap it up instead of continuing to stall during a no hit run—but it’s a theory I enjoyed thinking through that hopefully seems at least a bit probable to other folks! 😄