Blackman’s Coffin, the first in the Blackman Agency series by Mark de Castrique is free, and the next three series titles are discounted, right now, Feb 11, 2021, in both the US and UK. Prices are $1.99/£1.45 for the second title, The Fitzgerald Ruse; $2.99/£2.18 for the third, The Sandburg Connection; and $3.99/£2.88 for the fourth, A Murder in Passing. And the non-free ones are also eligible for VIP or coupon discounts at Kobo US. Some of these have multiple “editions” listed at some retailers, so use caution before you buy these – make sure you haven’t bought them before!
Note: the fourth title, Murder in Passing, although on sale at Kindle US and UK, doesn’t seem to be available at Kobo US. At least, I can’t find it…This is probably a glitch since the rest of the series is there, so if you really want it from Kobo US, I’d check back later.