Mariana Etista was a hotel employee who worked under Micah Sasucasa at the South American jungle. She had apparently received a call from Archie O'Logie before he was murdered so she was one of the four suspects of the case.
Etista was actually Diane Makepeace, the daughter of Keelan Makepeace. She came to a South American village three and a half years after her father died and had been engaged with a local named Chico Careta and started to teach him English as she was fluent in speaking the language. When a group of archaeologists led by world-famous Archie O'Logie came to their village, Careta became part of the group as their guide and at one dig, they found an ancient stone idol that was slightly cracked.
Etista wanted the stone idol and to get rid of Careta so she managed to "convince" him to kill O'Logie and obtain the stone idol. She participated in the plan by bringing up the glasses for O'Logie and Doug Scowers to drink Careta's liquor with at the storage hut. She came back to the hotel and later received a call from the intercom of the hut. She recognized the caller to be Careta, although he tried to impersonate O'Logie, and feigning fright, she had Sasucasa come up to the hut with her.
When they reached the hut, they found Doug drunk by Careta's liquor. Sasucasa found the hut to be locked so he had no choice but to force the door open. They found O'Logie's body with an axe lodged to his head but to their surprise, the corpse started walking to them. The corpse knocked over a bottle of liquor so she knew the walking corpse was not an illusion but the body eventually stopped moving. She later received the cracked stone idol. During the investigation of the archaeologist's death, the drunk archaeologist was detained and the investigation was closed afterwards.
News of the investigation being possibly re-opened due to a reconstruction device soon reached the hotel and Etista planned to get rid of Careta by having him arrested for murder. Under the pretense of bringing back souvenirs of England for the village, Etista convinced Careta to visit England. Like she predicted, the investigation, led by Inspector Alfendi Layton and Lucy Baker, led to Careta being the culprit. Careta admitted to the murder but soon found out Etista used him for her own purposes.
Before they started to question her, Etista fled the village along with the stone idol and later purposely tried to sell the stone idol, despite it having little monetary value. Interpol soon located her and alerted Alfendi and Lucy of Etista's hiding spot. Although they were warned of possible traps, nothing life-threatening was found during the search for Etista's secret room.
When Alfendi and Lucy found Etista, she was not wearing her Etista disguise. She briefly switched to Etista and switched back, revealing herself as Diane Makepeace. She told them about her murdering the Agonni family at the Merseyshore docks and soon fled through an old underground railway system.
- Her name is a pun on "marionetista", which means "puppeteer" in spanish, referencing the way she manipulates Chico Careta.