Stamets and Tilly try in vain to find anything special about the vial recovered from the ISS Enterprise, which contains just distilled water. But Burnham can link the sample to a Denobulan scientist, who was a member of Vellek's group and who used to build water towers on dehydrated worlds. On the pre-industrial planet Halem'no there is one still in operation. Burnham and Tilly can't beam directly into the tower, which is surrounded by an energy field. They join a group of Halem'nites on a pilgrimage to the "High Summit". As they arrive, they are greeted by Ravah and their father Ohvaz. They learn of the "Journey", a race whose winner is allowed to enter the High Summit to be with the gods. Adira finds out that there are four more towers on Halem'no that have stopped working, and that the last one is going to fail as well, unless it is serviced via an auxiliary control panel. Tilly and Burnham join the Journey, which starts with them having to ingest something that creates extreme thirst. Everyone drinking water during the run is disqualified. Burnham drops out intentionally because she thinks she has found the way to the control unit. As only Tilly and Ravah are left in the race, Ravah trips and drops their water bowl that they have to carry across the finish line, but Tilly shares her water with them so they can enter the tower with her. Having found the control panel, Burnham successfully repairs the tower. Tilly is shocked to learn that the winners are going to be sacrificed. She and Ravah are locked up in the tower where they will suffocate once it is active. Burnham decides to break the Prime Directive. She tells Ohvaz that she is from another world and convinces him to open the door so Ravah and Tilly can be saved. Tilly has discovered that one symbol inside the tower matches the one on the vial. It points to the fourth tower. The next puzzle piece is found there and leads to Betazed. In the meantime, the USS Locherer has found Moll and L'ak.

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