Verify sign error in Fowles 10.28 characteristic polynomial

Clear[m, p, lambda, d, f]
m = {{1-lambda, d}, {-1/f, 1 - d/f - lambda}} ;
m // TraditionalForm
p[lambda_] = Collect[Det[m], lambda] /. (-2 + d/f) -> -2 alpha

Solve[p[lambda] == 0, lambda]