Oxford time travel novels

For Kivrin, preparing an on-site study of one of the deadliest eras in humanity's history was as simple as receiving inoculations against the diseases of the fourteenth century and inventing an alibi for a woman traveling alone. For her instructors in the twenty-first century, it meant painstaking calculations and careful monitoring of the rendezvous location where Kivrin would be received. But a crisis strangely linking past and future strands Kivrin...

When a time-travel lab suddenly cancels assignments for no apparent reason and switches around everyone's schedules, time-traveling historians Michael, Merope, and Polly find themselves in World War II, facing air raids, blackouts, unexploded bombs, dive-bombing Stukas, rationing, shrapnel, V-1s, and two of the most incorrigible children in all of history--to say nothing of a growing feeling that not only their assignments but the war and history...