Our own insider has provided minor spoilers, which can be found here. ABC describes the episode as:

Desmond goes in search of a woman who could be the key to helping Faraday stop the island's erratic movements through time, and Locke discovers the identity of the unknown forces who have been attacking the survivors. Guest starring are Nestor Carbonell as Richard Alpert, Sonya Walger as Penelope "Penny" Widmore, Alan Dale as Charles Widmore, Rebecca Mader as Charlotte Lewis, Tom Connolly as Jones, Alexandra Krosney as Ellie, Imelda Corcoran as Abigail, Matthew Alan as Cunningham, Dan Hildebrand as custodian, Mary Ann Taheny as Moira, Raymond Ma as Efren Salonga, Sarah Farooqui as Theresa and Tuli Roy-Kirwan as secretary.

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