Five minds / Guy Morpuss.

The Earth's spiralling population has finally been controlled. Lifespans are limited to eighty years, except for those who make an extreme choice: to become a commune. Five minds sharing one body, each living for four hours at a time. But with a combined lifespan of nearly 150 years. Alex, Kate, Mike, Sierra and Ben have already spent twenty-five years together in what was once Mike's body, their frequent personality clashes leading to endless bickering, countless arguments, and getting themselves stranded on a Russian Arctic freighter. Wanting to buy upgrades for their next host body, they decide to travel to a Death Park where time can be gambled like money. But things go very wrong when Kate accepts a dangerous offer, and one of them disappears. Someone is trying to kill off members of the commune. But why? Is one of them responsible? Or is an outsider playing a deadly game? It's hard enough to catch a murderer. It's almost impossible when you might be sharing a body with them ...