Star Trek: DTI: The Collectors is an interesting time-travel tale. It opens on a planet were an obelisk is found and is determined that it needs to be looked at by the DTI the Federations temporal investigators. Not too soon after they get it back to the DTI vault then an uptime agent comes in and takes it and two DTI agents with her but instead of returning to her time they jump timelines and wind up in a universe were the Federation Temporal Agency is now the Temporal Intervention Agency and a fight happens putting two versions of the FTA agent herself but in the end working it out until the original takes them far uptime to the point of origin for the obelisk. This book is great and it shows us that the DTI is needed as well as gives us insights into the temporal cold war that appeared in Star Trek: Enterprise. If you like time-travel then I highly recommend this book.