I worked out a couple of issues while sleeping (I do my best thinking asleep so there's really not much point my attending meetups!). Instead of averting deaths, the class will be investigating a recurrence in the future of a mystery disease last seen in the past (and which they therefore have to investigate).
Students won't time-travel/teleport physically, they'll send spime swarms instead to act as telepresence surrogates. Unfortunately there's a limit on how far you can "jump" so students from the future can't get to the past themselves.
I know we're not doing narrative at the moment but when the time comes I'd like to ask whether plot twists are appropriate in ARGs or do they just confuse matters?
Anyway, apologies if this is all a bit arcane but I'm happier now taking this plot forward -- btw I have a fairly small digital footprint and can be found at https://twitter.com/#!/graymills as well as http://tidalblog.blogspot.com/ .