Online Diary System

Hi,
Building a site for financial adivsers appointments and need a plugin that does the following, any suggestions?
Allows each adviser to login under a unique ID and to block out times in a diary system without seeing other advisers diaries.
The owner of the business wants to be able to login select and view individual diaries for each adviser.
The owner also wants to add dates and times of new appointments to each individual advisers diary.

All sugestions welcome!