At the Temple Church in London, the dubious altar boy is convinced to let the fictitious "Sir Christopher Wren III" in to scatter his ancestor's ashes.
He's also the one who importantly informs Langdon, Sophie, and Teabing that the knights in the church were effigies, not actual tombs…so they were searching in the wrong place. Whoops.
This poor guy's interrogated by an irate Bezu Fache, and reveals that Teabing's plane is most likely headed to Biggin Hill airport (under threat of arrest, of course).
Bishop Aringarosa's the unwitting pawn of Teabing when he's drawn into his plot while trying to save his church, the sect called Opus Dei. Poor dumb dude.
He learns that his church's losing its prelature (read: cash flow and legitimacy) because the new pope is a more liberal-leaning Catholic who doesn't approve of Opus Dei's unorthodox, ultra-conservative practices. (It doesn't help that they'd earned their prelature thanks to their "financial munificence in 1982", which assisted the Vatican Bank with a very timely and hefty loan.)
So, when the mysterious Teacher contacts him with a way to save his church and his way of life, Aringarosa jumps at the chance.
He's also Silas's kind benefactor. He'd rescued Silas from the brink of death and taught him the Opus Dei way of life—thus earning an incredibly loyal companion. The Teacher (Teabing) recognizes how useful it could be to have an ultra-faithful man of past violence on his team, so Aringarosa and Silas are perfect to carry out his plan.
Bishop Aringarosa ends up helping to save the day, however, because he realizes that he's been duped and decides to come clean to Fache in time to absolve Langdon and Sophie, and help capture the elusive Teacher. Bravo, Bishop.
Sister Sandrine's a nun at the Church of Saint-Sulpice who's tragically murdered by Silas. Here's her bio, courtesy of Dan Brown:
As the church's conservatrice d'affaires, Sister Sandrine was responsible for overseeing all nonreligious aspects of church operations – general maintenance, hiring support staff and guides, securing the building after hours, and ordering supplies like communion wine and wafers. (7.2)
She was also secretly in the Priory of Sion, and her unique position of watching over the false keystone was what led to her unfortunate death. Womp womp.
Although he's Sophie's long-lost little brother, Dan Brown never gives him a name. But he looks like Sophie, and he's lived at Rosslyn his whole life, raised by Sophie's grandmother, Marie Chauvel. He seems like a sweet enough lil' bro.
This lovely lady is Sophie's grandmother, long presumed dead because of a pact that she and Sauniére had agreed upon for the protection of their grandchildren (and the Merovingian bloodline).
We bet she makes the best cookies, too.
This dude holds the title of Executive Services Officer at Biggin Hill Airport. He's reluctantly forced to comply with French authorities in their attempt to arrest Teabing and his guests upon landing at the airfield.
Langdon's literary editor. He unwittingly played a role in this caper because he sent Sauniére an advanced copy of Langdon's new manuscript, prompting Sauniére to request a meeting.
Pamela (we hope her nickname is "Go Gettum") is a librarian at the King's College's Research Institute in Systematic Theology. She helps Langdon and Sophie search their database in order to figure out Sauniére's clue about "In London a knight A. Pope interred".
This is the elderly Louvre security who "captures" Langdon…but ultimately lets him and Sophie flee due to Sophie's clever mastery of persuasion.
This is the guy who wakes Langdon up in his Paris hotel room because Collet is insistent upon gathering Langdon for Fache's investigation—no matter what.
This is the cop who forced his way onto Teabing's plane when it lands at Biggin Hill…and who basically gets himself into deep trouble when he doesn't follow the letter of the law in terms of being able to search someone else's private property.
Astronomer at the Pope's summer residence, and temporary guide for Bishop Aringarosa on one of his visits there.
The woman who introduces Langdon at his lecture in Paris, and who embarrasses him by reading from a recent Boson Magazine exposé.
Langdon's failed love interest from the previous book, Angels and Demons.