What is the nature of Antonia's phone call to Olivia and how does it change Olivia's plans with Hank?

Olivia receives a phone call from Antonia. She is coming to England because Cosmo has just passed away suddenly. She wants to stay with Olivia for a little while until she can figure out what to do. Olivia is shocked, but she also realizes that she needs to change her plans with Hank. She tells him that they will now go to visit Penelope at Podmore's Thatch.