Chapter 828 is titled "1 and 2".
Short Summary

Purin learns that the group she was talking to is from the Straw Hat Pirates while the Sanji retrieval team also learns that Purin is Sanji's betrothed. After explaining more about the Charlotte Family and her thoughts about Sanji, Purin shows the team a route to Whole Cake Island that will allow them to arrive undetected.

The Sanji retrieval team later returns to the Thousand Sunny but is unable to find Pekoms. They soon find a message telling them to turn back.

On another island, Sanji's two elder brothers lead Germa 66 to end a two-year war in four hours.

Long Summary

Luffy and the Sanji retrieval team are shocked to discover that Purin is not only one of Big Mom's daughters, but the daughter that has been engaged to marry Sanji. Purin, in turn, is equally shocked that the guests she had invited for tea were Sanji's crewmates. She asks them how they managed to get past Totland's tarte inspection, before warning them that they will be killed if Big Mom discovers their presence. However, she remembers that the Straw Hats are also famed pirates, and retrieves a knife to defend herself; Pedro in turn threatens Purin until Nami diffuses the situation.

The group discuss the situation over tea. Purin reveals that the Charlotte Family is compromised of 129 people (Big Mom, her 43 husbands, 39 daughters and 46 sons), and that Big Mom's children have all been raised to understand that she will arrange their marriages to grow the strength of her crew. However, one of Purin's sisters left Whole Cake Island to pursue a marriage for love, which attracts Nami's attention.

Chopper proceeds to ask Purin if she had met Sanji yet. Purin is flustered by the question and blushes, responding that she had met him once. She remarks on his gentlemanly mannerisms, his reputed strength, and their shared passion for cooking; however, Chopper has to correct her misconception that Sanji's epithet, "Black Leg", meant his legs were black. Luffy responds enthusiastically to Purin's admiration for Sanji, but when Nami asks Purin if she has fallen in love with Sanji, she becomes even more flustered and responds that it's irrelevant because Big Mom's commands are mandatory.

When Pedro suggests binding and gagging Purin to prevent her from revealing their presence in Totland, Purin draws a map for the Sanji retrieval team, revealing a secret route through Totland that would allow them to arrive onto Whole Cake Island undetected. She reflects that, despite everyone's excitement at the upcoming wedding, and despite her own happiness at finding Sanji so 'wonderful' and compatible, she did not want to stand in the way of his intention to return to the crew. The crew express great shock at the fact that Sanji turned down a woman - Luffy is so moved that he even cries - but Purin replies that seeing the crew's mutual commitment to Sanji helped her to decide that she did not want to marry someone who would spend the rest of his life regretting the marriage. She arranges to bring Sanji to rendezvous with the retrieval team on the southwestern coast of Whole Cake Island, but warns them that Big Mom will never willingly let Sanji go.

When someone comes knocking on the door, Purin helps the team sneak out. After purchasing some supplies, they return to the Thousand Sunny, only to find Pekoms missing and a warning to "turn back" scrawled in the bathroom. Unfazed, Luffy declares that things have finally gotten interesting, and that they will continue ahead.

Elsewhere, on Broccoli Island, Germa 66, led by the first two sons of the Vinsmoke Family, are shown bringing an end to its 2-year civil war after 4 hours. Angry that the Germa has taken everything from him, an opposing soldier attempts to shoot the eldest Vinsmoke son while his back is turned. However, he orders a Germa agent to take the bullet. He then twists the soldier's gun so that it points at the soldier's head, remarking that he has no concern for the soldier's family or the war, and that the war was going to make him late for Sanji's wedding. The Vinsmoke then executes the soldier. Meanwhile, the second Vinsmoke son retrieves the compensation paid by the 'victorious side' to Germa for its assistance in defeating their enemies. The two Vinsmokes then contact an unseen individual via Den Den Mushi and learn that Sanji has already arrived on Whole Cake Island. The elder Vinsmoke comments that he can't wait to see Sanji again, but is called out as a liar by the other. They promise to arrive on Whole Cake Island on the day before the wedding.

The two Vinsmoke brothers are finally shown standing atop a building and surveying their destruction of the city, as Germa 66 is hailed by the populace it had 'saved'.

Quick References

Chapter Notes

The Sanji retrieval team learns that Purin is Sanji’s bride-to-be.
Purin explains that Big Mom uses her children’s marriages to strengthen her pirate crew.
The Charlotte Family is composed of 129 nuclear relations to Big Mom.
Big Mom has 43 husbands, 39 daughters (including Purin), and 46 sons, as well as grandchildren.
Purin mentions a sister who left in order to find a husband on her own.
Purin states that she already met Sanji once before and that he turned her down.
Purin shows Luffy’s group a route to Whole Cake Island that would allow them to arrive undetected.
A way to navigate using each individual pose on the New World log Pose, instead of the needle, is introduced.
Luffy's group returns to the Thousand Sunny, but Pekoms is nowhere to be seen and a message telling them to turn back is left behind.
Sanji’s two older brothers are introduced (although their names remain unknown).
They stopped a two year war on behalf of Germa 66, in exchange for compensation.
Their appearance is similar to the Germa 66 agents from Vito's flashback in Chapter 825, apart from the colors of one of their capes.